What is metrication?

Metrication is the process of switching from the use of an incoherent collection of countless historical and parochial weights and measures to the use of a single, coherent, standard system of weights and measures known as the metric system.

More recently, it has come to refer more specifically to the process of converting to the use of the modern iteration of the metric system – the International System of Units (SI).

Since its initial development in the 1790s, the metric system has become the world’s standard system of weights and measures.

Every country in the world has adopted the metric system for some or all official purposes. However, while most countries have now completed metrication, a few, including the UK, have yet to adopt the metric system for all official purposes.

In those few countries where old measurement units continue to be used, such as yards and miles on British road signs, the old units are now legally defined in terms of metric units. Thus, for most purposes, the metre is not permitted to be used on UK road signs to indicate distance, unless it is shown in multiples of 0.9144 m, and labelled as “yards”. (One yard is defined as 0.9144 m).

What is the metric system?

Officially known as the International System of Units (SI), the metric system is the international standard system of measurement. It is based on the standard decimal number system, and is designed to be easy to learn, and simple to use.

In everyday use, it is used to measure road distances and speeds, floor areas, storage volumes, energy use, and the mass and volumes of food and drink.

It is also used to measure temperature, electricity and the brightness of light bulbs. It is the standard system of measurement for all trade.

Units of measurement in the metric system relate to each other in a logical and coherent manner. Each quantity has one unit to measure it. Standard metric prefixes can be combined with any metric unit to form subunits which are multiples or submultiples of 10. All calculations using metric units are as straight forward as any other calculation using decimal numbers.

The metric system is based on properties of nature:

• The distance from the North Pole to the Equator is 10 million metres, or 10 000 kilometres.
• 1 metre can be divided into 10 decimetres, 100 centimetres or 1000 millimetres.
• 1 m = 10 dm = 100 cm = 1000 mm.
• 1 litre is the volume of a cube with sides of length 1 dm, or 10 cm.
• 1 kilogram is the mass of 1 litre of water.
• Water freezes at 0 degrees Celsius, and boils at 100 degrees Celsius.

Since its original inception, the metric system has evolved to become a single coherent system used for measurement in all fields of human endeavour, including science, medicine, technology, industry, commerce and sport.

Why metricate?

There are many reasons in favour of adopting the metric system in place of old non-metric units of measurement, and, no less persuasively, there are no good reasons for converting in the opposite direction.

Global standard

A single rational system of measurement units used throughout the world is vital to the smooth operation of international trade. The metric system is the international standard for weights and measures.

Mont Follick, House of Commons debate on the Decimal System – 12 May 1953

Ease of use

In contrast to imperial weights and measures, the metric system is easy to use. Its principal units and prefixes can be taught in a single school lesson. Other than the multiples of 10 and 1000 associated with the system’s prefixes, there are no conversion factors to learn.

For example, to measure length in imperial units, one needs to be familiar with inches, feet, yards, chains, furlongs and miles, together with a host of factors used to convert between them, such as 3, 8, 12, 22, 36, 1760, etc.

In contrast, in the metric system, length is measured using one unit – the metre, with the option to use prefixes when numbers become cumbersome on account of being very small or very large. As a consequence, calculations using metric units are as simple as any other numerical calculations.

Scalability and understanding

All metric measurements scale seemlessly from the very small, to the very large. Using metric units, it is easy to see the relative sizes of things, which in turn enhances understanding of our surroundings. For instance, it is easy to see that 7 kilometres is ten times as far as 700 metres, whereas it is not immediately apparent how many miles a distance ten times as far as 700 yards would be.

Education

Metrication removes the need for school children to learn the countless conversion factors used to carry out arithmetic with non-metric measurement units. Long division of quantities expressed in multiple imperial units is a disheartening exercise, and time spent on such activities could be freed up for the study of much more interesting and profitable fields of mathematics.

Earl Fortescue, House of Lords debate on the Metric System – 21 July 1864

In 1895, a government report indicated that the continued use of imperial units in education was holding back children’s education. The report, by the Select Committee on Weights and Measures, estimated that “no less than one year’s school time would be saved”, if the metric system was taught in schools in place of the imperial weights and measures used at that time.

Single system

The need for a single system of measurement for all official purposes has been recognised since at least 1215.

Magna Carta – 1215

In 1862, the Select Committee appointed to consider the practicability of adopting a Simple and Uniform System of Weights and Measures, reported that, excluding the occasional use of the metric system, the UK had “no less than ten different systems of Weights and Measures, most of them established by law.”

Select Committee on Weights and Measures – 15 July 1862

If traders are free to choose different measurement units, price transparency is impossible. Consumers are forced to learn conversion factors, and must carry out tedious arithmetic in order to compare prices.

If our road signs use different units for speed limits and distances from the rest of the world, our cars have to be fitted with cluttered instruments with more than one measurement scale, in order for us to be able to drive internationally.

The Department for Transport have proved that it is impossible to maintain the use of a single non-metric system of measurement for road signs. After many years of resistance, the need for metric units on restriction signs became irresistible, resulting in the introduction of mandatory dual unit signs in 2016. The unit of speed used in digital tachographs and vehicle speed limiters is km/h, which means that road speeds also now use two measurement systems.

The only measurement system option available that can be used as a single official measurement system is the metric system.

Why completing metrication matters

Following a gradual adoption of the metric system beginning in the 19th century, with rapid progress in the 1960s and 1970s, the UK has for many years now been stuck in a measurement limbo, with metric being used almost exclusively for a large variety of purposes, but with old imperial units still in use for others – most notably for road signs.

Is the use of two systems an advantage?

When arguing against the completion of metrication, opponents sometimes claim that the UK’s current muddled use of metric units for some things, and imperial for others, gives us an advantage that should be envied when it comes to measurement, in that it somehow makes us ‘bilingual’ in both systems. This alleged ability has even been said to be our ‘superpower’, a skill unique in the world, that allows us to move effortlessly between imperial measurements and standard metric units, and as such we should not be seeking to give it up by completing the switch to the exclusive use of the metric system for all official purposes.

The reality of course is very different. As a YouGov survey (commissioned by the UK Metric Association in 2013) showed, British people in general have a poor knowledge of both systems, but understand metric marginally better. A key finding of the survey included the fact that 76% of respondents (including 95% of the 25-39 age group) were unable to answer correctly, or at all, how many yards there are in a mile.

There is also plentiful anecdotal evidence that, despite the sale of groceries being almost entirely in metric units for over 20 years, many people today remain unable to comprehend a weight loss when expressed in kilograms. The continued personal use of stones and pounds for body weight has led to the loss of any ability to compare weight loss to the weights of common foodstuffs.

Does the use of two systems give us freedom?

Ignoring the fact that this is never raised as an issue in countries that have been 100% metric for many years, some have argued that the continued use of two systems is an issue about freedom of choice – people should have the freedom to choose which system of measurement to use, they say.

No one would argue against freedom of choice in one’s own home, but for official purposes this is a false argument. If freedom of choice of measurement units is granted for trade, it is the salesman that chooses, not the customer. If different traders use different units, the customer loses the ability to compare prices easily.

With two systems in use at the same time, the only way to protect consumers is to require all traders to mark all goods in both systems. The use of two systems gives no one more freedom. It just creates more work for traders, and the increased clutter on labels makes price comparisons less straight forward for consumers.

In contrast, the use of a single universal system of measurement enhances a customer’s freedom to make informed choices about purchases.

Similarly, with the units used on road signs, road users have no freedom to choose the units used – these are chosen by the Government. If the Government chooses to continue to use yards and miles, road users are forced to understand two systems in order to be able to travel internationally. Switching all road signs to metric units will mean that road users will only ever need to be familiar with one system of measurement when driving anywhere in the world outside the USA.

Dual units in the media

Rather than adopting a policy of transition from the use of old imperial units to the use of modern metric units, some providers of news and weather forecasts have chosen to use dual units indefinitely. On websites with dual units, virtually every mention of metres is accompanied by a bracketed value in feet, every mention of Celsius is accompanied by a value in Fahrenheit. This, they would argue, keeps everyone satisfied.

Again, this is a false argument. It assumes that the avoidance of choosing one system over another is the only consideration when choosing measurement units. It pays no regard to legibility or comprehension. It also creates a new dilemma, which doesn’t exist when using metric-only. By choosing to use dual units, the wishes of those who prefer single units are ignored. Many find it irritating to constantly have to pick out values from measurements given in two systems at the same time. Apart from the obvious sensible reasons to stick to metric units, the use of dual units is probably alienating a large proportion of the target audience.

In recent years, the failure to complete the national metrication programme as a whole has encouraged some to regress to using dual units, having previously been metric-only.

For example, in the 1990s, some local radio stations switched away from the exclusive use of Celsius, and adopted a practice of quoting all temperatures in both degrees Celsius and Fahrenheit. This had the consequence that a string of temperatures given in dual units required more attention from the listener than the previous shorter list of single values. The knock-on effect was that it became easier for none of the information to be remembered at all, especially if a listener was busy with other tasks at the time of listening.

Incompatible units used for comparison

The description of goods is not fully covered by current weights and measures legislation. This has led to the anomaly where some products can continue to be described using measurement units that are no longer authorised for trade. If traders use different units to describe similar goods, the ability of consumers to compare products is adversely affected.

For example a refrigerator’s capacity might be described in cubic feet in one situation, but in litres in another, making it difficult to compare products.

Similarly, estate agents commonly describe room dimensions in feet and inches, and floor areas in square feet, even though furniture is sold in metric sizes, and carpet prices are quoted per square metre. The use of two systems here makes it difficult for anyone looking at new properties to estimate furniture requirements and costs for new carpets.

The square foot and cubic foot are units not authorised for trade, but are permitted for product descriptions.

Extending weights and measures legislation to cover product descriptions, and real estate details, as part of a programme to complete metrication, will enhance general comprehension and benefit consumers.

Incomprehension

In all walks of life, effective communication about dimensions and quantities requires everyone to use the same measurement units. Although some people are familiar with both metric and imperial units, the continued existence, and in some cases the official recognition, of two different and incompatible sets of measurement units leads many people to become more familiar with one set of units than the other. While many people use metric only, the failure to complete metrication inevitably means that some continue to use imperial only. The result is mutual incomprehension and breakdowns in communication.

Accidents and public safety

Accidents can occur as a result of the existence of two systems. Sometimes these can be extremely costly, or dangerous. If two parties in a transaction routinely use different systems, specifications given by one can easily be misinterpreted by the other.

• The most infamous example of this is the loss of NASA’s Mars Climate Orbiter in 1999. This was caused by a misunderstanding between NASA, who were using metric units, and its contractor, Lockhead, who were using US customary units. The specifications for thrust in newtons were mistakingly interpreted as pounds-force. The result was that the spacecraft entered orbit around Mars at the wrong altitude and burned up in the Martian atmosphere.
• Similarly, in 1983, an Air Canada Boeing 767 ran out of fuel because the refueling requirements had been mistakenly assumed to be in pounds, when they were actually in kilograms.
• When medical doses need to account for body weight, calculations are always carried out using kilograms. The potential for life-threatening dose errors to occur was highlighted by an exchange in the House of Lords on 25 February 2010, when peers drew attention to the residual use of imperial units for weighing in some parts of the National Health Service.

Numerous domestic incidents happen all the time. e.g.

• Measuring a window in inches to place an order for new curtains over the telephone, only to receive the goods with dimensions in centimetres.
• Asking someone to get a 2-litre bottle of milk, but they purchase a 2-pint bottle by mistake.

Most domestic accidents would not be classed as serious, but the potential for them to happen at all continues only because metrication has not been completed.

Conversion errors

In a situation where two incompatible measurement systems are in use, with some people using one system and other people the other system, it is sometimes necessary to provide conversions – for example, in news reporting, recipes, DIY instruction manuals. In other cases, carpenters, dressmakers or cooks may do their own conversions. Inevitably, mistakes sometimes occur. Particularly error-prone are Celsius to Fahrenheit conversions; and the process for converting “miles per gallon” to “litres per 100 km” is arithmetically challenging.

Enforcement

Currently, almost all retail trade is carried out in metric. However, following encouragement from government to not fully enforce weights and measures legislation, some small market traders continue to sell loose goods using units that are no longer authorised for trade.

A renewed committment to properly enforce legislation, as part of a process to complete metrication, would be in the interest of consumer protection.

Costs

It is not possible to put a definitive figure on the cost of having to operate in two systems. Undoubtedly, however, there are costs to manufacturers, retailers and others in having to provide two sets of information. In some cases, computer programmes will make the conversions automatically, but especially for small traders and for non-repetitive operations, the cost – even if only in wasted time and effort – must be significant.
Other costs can sometimes be precisely quantified: the cost of the lost Mars Climate Orbiter was given by NASA as $655 million. The Department for Transport has also estimated the cost of bridge strikes resulting from foreign HGV drivers not understanding imperial units as £234 000 annually without taking into account the cost of delays to road users, which are noted as being “non trivial”.

Failure to reap the benefits of investment in metrication

In past decades, considerable resources have been invested by both public and private sectors in metrication:

• Industry has upgraded machinery in factories and retrained their staff.
• Food manufacturers have adjusted to to new package size requirements.
• Retailers have purchased new metric scales.
• Schools have replaced textbooks, and adjusted to changes in the curriculum.

Unfortunately, much of this investment continues to be wasted. The most visible example of this is when school children, who have used metric throughout their school years, are faced with the need to become familiar with imperial units when they are old enough to learn to drive. At a time when their knowledge of metric units should be reinforced with practical experience, young people experience a pressure to forget metric units.

Peer pressure, reinforced by main stream media, also encourages people to measure their body weight in stones, and ignore the kilograms they learn in schools. This negates the ability to compare weight losses with common foodstuffs such as 1 kilogram bags of sugar.

Perception of the UK from abroad

Visitors to the UK cannot fail to notice the odd mixture of measurement units used in the UK:

• litres at petrol stations, but miles on road signs,
• square metres in carpet stores, but square feet on office space hoardings,
• kilograms for food, but stones for personal body weight.

Some may find it amusing, but others may take a more serious view and conclude that the UK is not fully committed to basic international standards for trade. The effects of this on inward international investment can only be detrimental to the UK’s prosperity.

The potential for such unfavourable perceptions can be avoided very easily with the introduction of a short programme of legislation to complete the UK’s metrication process.

Progress

Since the industrial revolution, the UK has been a leading country in technological progress. The average standard of living has improved markedly in the last two hundred years as a result. People have come to expect improvement, and not only have they grown to accept change, they actively seek out the latest innovations in consumer gadgets, and the latest upgrades of software applications.

However, the UK’s political institutions have not reflected the peoples’ eagerness for improvement when it comes to measurement units. Essentially, it has taken more than 200 years for Parliament to upgrade the country’s most fundamental technology – its system of weights and measures, and the process has still not been completed.

Metrication in the UK has been a very sporadic process. Some sectors have been fully metric for decades, whilst others such as road signage, have barely begun.

Examples of the current status of metrication

	Food and drink:	99% complete
	Post Office:	100% complete
	Construction:	99% complete
	Industry:	100% complete
	Farming:	100% complete
	Estate agents:	5% complete
	Road signs:	5% complete

19th Century

Throughout the 19th century, numerous reports recommending the change to the metric system were published. There was also considerable political enthusiasm for the switch to the metric system, along with decimal currency. From at least the 1860s, it was the policy of successive British governments to allow the use of metric units of measurement. However, despite this governments in the 19th century were ultimately unable to enact the legislation necessary to make meaningful progress in switching to the metric system.

In 1864, the Weights and Measures (Metric System) Act 1864 rendered permissive the use of the Metric System of Weights and Measures.

On 26 July 1871, the Government lost a Bill to make metric compulsory after two years, by only 82 votes to 77 votes.

In 1895, a Select Committee of the House of Commons took exhaustive evidence on the subject of adopting the metric system. Their Report, made three key recommendations:

• that the metric system of weights and measures be at once legalised for all purposes
• that after a lapse of two years the metric system be rendered compulsory by Act of Parliament
• that the metric system of weights and measures be taught in all public elementary schools as a necessary and integral part of arithmetic

In 1896, following an extensive debate, the House of Commons voted unanimously to legalise the use of metric for all purposes.

20th Century

In 1904, following a campaign led by Lord Kelvin, a petition with signatures representing over 3 million people was presented to the House of Lords on the occasion of the Second Reading of Lord Belhaven’s Metric Bill. The House of Lords responded by voting unanimously to make metric compulsory in place of imperial after two years. The Decimal Association cited the names of 333 MPs in favour of the reform. However, the House of Commons failed to adopt the Bill.

Throughout the 19th and early 20th centuries, the UK played an important role in the development of the metric system. Its modern iteration, the International System of Units, or SI, has six units named in honour of British scientists.

From 1 May 1914, all air pressure data in the Met Office’s Daily Weather Reports were in millibars. The millimetre was also formally adopted for the measurement of rainfall, as was the metre per second for the measurement of wind speed. However, at the time, the Beaufort scale continued to be the main unit used for the expression of wind speed in weather reports.

In 1950, the Hodgson Committee on Weights and Measures, which was set up to review legislation, unanimously recommended compulsory metrication and currency decimalisation within ten years. Their report said:

 
On 1 January 1961, the Met Office formally adopted the degree Celsius as the official unit for the measurement of temperature. This followed the adoption of the unit by the World Meteorological Organization as the standard unit of temperature measurement.

In 1963, the British Standards Institution (BSI), after consulting with British industry, came down firmly in favour of starting the change. The then Federation of British Industries wrote to the Government saying that the vast majority of their members, both in the number of firms and in the total size of their businesses, was in favour of adopting the metric system as the primary, and later as the only, method of measurement to be used in Britain. In 1965, the Government accepted that recommendation.

On 24 May 1965, the Government announced its intention that, within 10 years, the greater part of the country’s industry should have changed to the metric system.

Throughout the 1960s, the BSI worked with the International Standards Organisation (ISO), and with the UK’s European neighbours, to push for the international adoption of the newly-defined SI units, in place of older metric units. International agreement on which metric units to use was important for the future development of standards. It was recognised that a broadening set of common international standards was important for the UK’s future prosperity.

In May 1967, at a tripartite meeting between the UK, France and West Germany, it was agreed to phase out the use of the calorie, the thermie and the frigorie, in favour of the joule. The BSI also sought to phase out the international use of the kilogram-force in favour of the newton. In 1971, these objectives were accepted by the European Community, and included in a new European Community Directive on Measurement Units.

On 26 July 1968, the Government accepted the recommendation that a Metrication Board should be set up as soon as possible, and affirmed that the target date for the completion of the metrication programme across all sectors would be the end of 1975.

On 5 March 1969, the Government announced that speed limits would go metric in 1973. Speed limits on road signs would switch from miles per hour (mph) to kilometres per hour (km/h). However, on 9 December 1970, the new Government postponed the switchover date indefinitely.

In November 1970, shortly after the election of the new Government, the Secretary of State for Trade and Industry stated that no new legislation would be made regarding metrication until the Government had set out its policy in a forthcoming White Paper on Metrication.

On 22 December 1970, an agreement was reached with the EEC that, following its forthcoming accession to the EEC in 1973, the UK could continue to use non-metric units for legal purposes until the end of 1979. This allowed the UK to proceed at its own pace, and gave plenty of time to set its own schedule for the completion of metrication.

By 1972, the construction industry had substantially completed its metrication programme, and metrication of industry had begun. British Steel switched in April 1972.

In February 1972, the Government published its White Paper on Metrication. This initiated a metrication programme in the food sector. Beginning with metric packaging in 1973, the programme was set to complete in 1978, but important legislation was delayed which meant that food was not fully metric until 2000.

In 1974, metric units were added to size labelling on clothing.

In February 1975, retailers of fabrics and carpets began selling in metric units on a voluntary basis. In the case of carpets, this initiative eventually failed when one large retailer reverted to imperial pricing – something that follow-up legislation could have prevented.

From July 1975, over a period of 18 months, agriculture and horticulture switched to metric.

On 29 September 1975, the Post Office switched to metric scales and metric units for all postal tariffs.

On 14 November 1979, the new Government announced the abolition of the Metrication Board. The Minister for Consumer Affairs, Sally Oppenheim, wanted all further metrication to be on a purely voluntary basis. The consequence was that progress on metrication ground to a virtual halt in the middle of what should have been a short transition phase. The situation with food in particular forced consumers to deal with a dual unit muddle for 20 years.

In 1994, legislation was finally introduced to complete the switch to metric units for almost all economic, public health, public safety and administrative purposes.

From 1 October 1995, all remaining imperial units ceased to be authorised, except for a few specific uses including the pound and ounce for goods for sale loose from bulk, the pint for draught beer and doorstep milk deliveries, and imperial units for speed and distance on road signs. Foods pre-packed in variable weights such as cheese and meat, were now required to be sold in metric units.

21st Century

On 1 January 2000, all goods sold loose from bulk were required to be weighed and sold in metric units – ounces and pounds were no longer authorised, but could be used as optional supplementary indications.

Withdrawal of non-metric units

A necessary element of metrication is the withdrawal of the legal authorisation of non-metric units. The reduction in the number of legally authorised measurement units began well before the 1960s, when metrication began in earnest.

Withdrawal of authorisation of imperial units

Completion of metrication

Clearly, much progress has been made, especially where national programmes have been able to be coordinated centrally by the likes of the Metrication Board. For many years, for most practical purposes, it has been accurate to describe the UK as a metric country. However, the few tasks that still remain for the UK to complete its switch to metric units for all official purposes are highly visible, and prevent the full benefits of having a single rational measurement system of measurement for all official purpose. In particular, the use of imperial road signs in a metric country is always difficult to explain to visitors from abroad, and contradicts the notion of a Global Britain.

What needs to be done?

Before metrication can be completed, politicians and civil servants need to recognise that there is a problem. The current muddled official use of measurement units has remained unchanged for so long now that many people accept it is normal. Only when the existence of the problem is acknowledged, will it be possible for it to be resolved.

The following is a short list of tasks that any government would need to carry out for the UK to complete its switch to the use of metric units for all economic, public health, public safety and administrative purposes: