Briefing note

UKMA has prepared a briefing note for those who might find themselves putting the case for completing the metric changeover or speaking on behalf of the Association. Many of those who have read the note have suggested that it deserves the widest possible circulation. It has therefore been posted on this web site. Who knows – one day it could be you in front of the TV camera!

Briefing note for UKMA representatives

The purpose of this note is to set out the key points that UKMA representatives should try to get across in any contact with the media (radio or television interviews, letters to newspapers or online comments).

It comprises two parts:

(a) Key points to get across:

  • Need for a single system that everybody uses
  • Reasons why the metric system is better than alternatives
  • It’s in the UK’s national interest – not a European issue.

(b) Suggested responses to hostile questions and arguments.

Key points to get across

  • Every country needs a system of weights and measures that everybody understands and uses for all purposes.  What we don’t need are two systems, with some people using one system, others using a different system, with resulting incomprehension, mistakes, conversion errors, accidents1 and increased costs. Therefore we should standardise on one single system.
  • The metric system is preferable to imperial units because
    • It is mainly decimal2 – hence, easy to work with (counting in tens), e.g. there are 1000 litres in a cubic metre, 100 hectares in a square kilometre.
    • It is the world system – used by countries inhabited by 95% of the world’s population (the main exception is the USA – but see C below)
    • Most of our imported manufactured goods are made to metric dimensions. Similarly, our exports have to be metric to satisfy foreign customers. Hence it would not be possible to do without metric, whereas we are the only3 country that uses imperial.
  • Metrication is in the British national interest and is not a European issue. UK started to go metric in 1965 before entry to EEC (in 1973). Contrary to the widely-believed myths promoted by Eurosceptic media, the EU has never tried to impose metrication and has always agreed any request for delays, derogations, etc, culminating in 2009 decision to authorise imperial units indefinitely for various purposes in the UK.

1 e.g. Mars Climate Orbiter, Gimli Glider

2 but see N below

see C below

Suggested responses to hostile questions and arguments

A. Imperial units are natural whereas metric units are arbitrary.

  • Imperial units are only “natural” in the sense that it is “natural” to speak English. In other words, it is just what you are brought up with. People in countries that use the metric system think metric units are “natural.”
  • Units based roughly on body parts may have been adequate in medieval times, but are not appropriate for modern manufacturing or commerce. They have to be precisely defined and hence cease to be “natural” and are just as arbitrary as metric units.
  • [Actually, metric units are natural in the sense that they are defined by constants of nature, e.g. speed of light. (Care with this argument – only use with an interviewer or audience that is likely to understand the issue)]

B. Metric system results in absurdly large numbers, e.g. 910 mm bust size.

  • This is the fault of the user. The metric system is flexible, so this could have been expressed as 91 centimetres.  Anyway, imperial also uses large numbers, e.g. aircraft height of 20 000 feet (which could be expressed as 6 km).

C. Our biggest trading partner, the USA, uses imperial units (or “English” units/the same units as Britain).

  • Not true. US Customary units are not all the same as imperial – especially pints, quarts, gallons and fluid ounces are all different. Americans don’t use stones or hundredweights, and their ton is 2000 pounds. In packaging they also usually decimalise pounds rather than use ounces.
  • Key parts of the USA are metric, e.g. the Federal Government, the Military, NASA, some industries, notably the car industry. Metric units are permitted on road signs, and frequently appear on retail packaging, e.g. groceries.
  • The USA is not our biggest trading partner (only about 11% of the total). The EU is by far our biggest trading partner (our trade with Germany alone exceeds that with the US).

D. Nevertheless, the Americans manage alright with two systems. Why can’t we carry on doing the same?

  • The American situation is different from ours. Their metrication programme started 10 years after ours, and didn’t get so far before it was aborted. Thus, although there is considerable metric usage in the USA, it is mostly hidden. An average American, unless he/she is in the armed forces, or works for NASA or in the car industry, can therefore manage daily life without using any metric units.
  • By contrast, in order to function effectively in the UK, you need to know both systems.  This is wasteful and confusing.

E. OK – if we need to standardise on one system, why not go back to imperial?

  • It would not be practical to phase out metric units. If we want to engage in international trade, we still have to accept imported goods packaged and manufactured in metric units. Scientific research and education is dependent on metric units.  It would also be very expensive to reverse all the progress that has been made in the last 50 years. Conversely, it would be a simple matter to adopt metric units for the few remaining imperial uses (road signs, draught beer, doorstep milk and advertising/product description).

F. The Americans put a man on the Moon using imperial units.

  • The underlying science was developed using metric units.
  • The Lunar Module’s onboard Apollo Guidance Computer used metric units for the computer-controlled phases of the spacecraft’s descent to the surface of the Moon.
  • The Russians put the first satellite in space (Sputnik 1) and the first person in space (Yuri Gagarin). The systems that competed in the space race were economic not measurement.
  • NASA has now gone metric for future space projects where these are not based on existing designs.

G. It would be more trouble than it is worth to complete conversion.

  • The primary remaining tasks for the Government are the conversion of road signs and making changes to Regulations to require metric units to be used in advertising and product description.  Neither would be particularly difficult or troublesome.
  • It would be very worthwhile since British people would then not need to be familiar with two different and incompatible sets of measurement units.

H. Europe has given up trying to force Britain to go metric, and therefore we are free to use our own weights and measures.

  • The EU (formerly EEC) has never tried to force the UK to adopt the metric system for internal matters, and has always agreed that we can keep imperial units alongside metric for as long as we like.
  • For cross-border trade there has to be a common system, and all member states have to follow the EU rules on labelling.

I. People should be free to use whatever units they like.  What’s wrong with having two systems?

  • People have never been allowed (since 1824) to use any units they like.  It is essential to commerce and industry that there is a robust system guaranteed by the state.  It is also essential for consumer protection.  Allowing two (or more) systems is a recipe for misunderstanding, mistakes and fraud.
  • Magna Carta – England’s first Bill of Rights – sought to protect consumers by limiting choice of measurement units.

J. Many countries have more than one language (e.g. Switzerland, Belgium), but nobody argues for one standard language.  Isn’t the same true of measurement units?

  • These countries have a single measurement system – metric.
  • When people in these countries talk to each other, they only use one language at a time, e.g. in the Flanders region of Belgium, all official business is in Flemish exclusively.

K. Duodecimal system is superior to decimal, since there are more factors (2, 3, 4, 6) whereas decimal has only two (2 and 5).

  • Our numeral system is decimal, and it is logical that the measuring system should be aligned with the numeral system.
  • The duodecimal system does not permit division by 5 or 10.
  • Most imperial ratios are not duodecimal – viz. 14 pounds in a stone, 3 feet in a yard, 1760 yards in a mile, 16 ounces in a pound, etc.

L. Counting in tens ‘dumbs down’ people’s arithmetic abilities, and leads to poorer maths skills.

  • The evidence4 is that students in metric countries have better maths skills – whereas both the UK and the USA lag behind.  This could be because students in metric countries do not have to waste time memorising and practising conversions.
  • Also evidence from pre-1970 that doing “sums” (e.g. converting pounds to ounces, or square inches to square feet) puts kids off essential STEM subjects (science, technology, engineering and maths).

M. The decimal system is error-prone because of misplaced decimal points.

  • Imperial units can be subject to the same errors.  Non-decimal ratios make calculation more difficult and introduce an additional source of error.

N. What about time? You can’t metricate that!

  • The metric unit of time is the second (which is subdivided into milliseconds etc).  The minute, hour, day and year are not metric units but are non-decimal units accepted for use with the metric system.  This is obviously because the length of the day and the year are determined by the laws of physics and do not lend themselves to decimalisation.

O. Imperial units are traditional and part of British culture – why should we throw away our culture and adopt foreign measurements?

  • The mile (mille passus) and the pound (libra = lb) are of Roman origin, the ounce (oz) Italian or French (avoirdupois), the acre Saxon (cf. Acker – the German for field).
  • Imperial units were only standardised in 1824 (more recently than some metric units).
  • British scientists and engineers helped to develop the metric system – which is why 6 units are named after them (watt, newton, joule, farad, kelvin, gray)
  • Countries that use the metric system still retain their individual cultures.  The Brazilians are no less Brazilian, the Japanese no less Japanese for using metric units.
  • Going fully metric will not affect cricket, Beefeaters, kilts and haggis or the eisteddfod, and Shylock will still demand his “pound of flesh.”

P. The laws of many sports use imperial units e.g. the “18 yard box” in football.

  • The controlling bodies for sports that are played internationally (e.g. IOC, RFU, FIFA, R&A) use either metric units only or metric units alongside imperial units, e.g. in football the penalty area is defined as 16.5 metres or 18 yards.  The only sports that do not use metric units are those that are played primarily in the USA, e.g. baseball and American football.

Q. International aviation is not metric – feet are used for altitude and knots for speed.

  • International agreements for aviation include a mixture of metric and non-metric units. For example, metric units are replacing ‘inches of mercury’ for the measurement of pressure, which is used for calibrating barometric altimeters.
  • The international nautical mile is defined as 1852 metres exactly. The UK Hydrographic Office adopted this definition and dropped the UK definition of 6080 feet in 1970.
  • Many countries use metres for altitude and km/h for speed. In particular, China, which runs the second largest aviation transport system in the world, Mongolia, Russia and ten other states that were created when the Soviet Union was dissolved.
  • The importance of vertical separation for safety in air transport, and the difficulties resulting from the use of two units of measurement for altitude show the importance of universal standards. Moving towards a single unit for altitude is a long term objective of the International Air Transport Organisation (IATO).

R. Metric units are all very well for science and industry but are not user-friendly for everyday life.

  • The flexibility of the metric system means that metric units can be used for everyday purposes, e.g. grams, kilograms, litres, millilitres, centimetres are all appropriate for the kitchen;  watts and kilowatts are suitable for light bulbs, electric motors, car engines and central heating systems;  hospitals weigh babies in kilograms.

S. British people don’t understand metric units.

  • Most British people will have been taught the principles of the metric system at school.  These principles are very easy to learn.
  • Familiarity with metric units comes from using them.  Thus if people have to use metric units, they will quickly adapt.
  • When British people drive in continental Europe, they very soon adjust to dimensions in metres, distances in kilometres, and speed limits in kilometres per hour.
  • British people ARE familiar with many metric units, e.g. W and kW for electrical goods, kWh for energy, litres for fuel and soft drinks, kg for airline luggage weight limits, g and mg for drug prescriptions.
  • British people were well able to understand the all-metric Olympic Games.

T. Metrication is so unpopular that no politician will risk losing votes by supporting it.

  • There is no evidence that metrication is an important factor in people’s voting decisions.  It has not figured in any general election campaign.
  • It is politicians, newspapers and commentators with their own agenda who talk about it.  Most people are indifferent to the issue, and many would welcome its resolution.

U. Metrication is too expensive and not value for money.

  • Most of the costs of metrication have already been incurred, e.g. in retooling factories, rewriting school textbooks and exam syllabuses, re-calculating prices.  The main remaining cost is for road signs, most of which could be phased in with natural replacement at nil or low cost (distance signs).  The cost of amending speed limit signs is estimated at £20 million – a tiny amount compared with the UK Department for Transport (DfT) budget.
  • The benefit of completing metrication is that the UK would no longer have to muddle through with two incompatible systems of measurement.

V. Converting road signs would divert scarce resources from high priority transport projects.

  • Transport priorities are very controversial (e.g. airport runways, high speed rail, widening motorways) and cost billions of pounds.  The cost of converting road signs is tiny by comparison with the enormous sums that the DfT routinely wastes, e.g. £80 million plus on the West Coast Main Line rail franchising fiasco.
  • Completing metrication is really a weights and measures project – not a transport project, and should not be compared with normal transport infrastructure projects.  However, it should still be funded from the transport budget since all other sectors have had to absorb their own metrication costs, and it would be unfair on them to make Transport a special case.

W. Even metric countries still use some imperial units, e.g. plumbing, car tyres, TV screens.

  • In these examples, the imperial units are not being used for measurement.  They are simply descriptions or standard sizes – similar to a size 12 dress or a size 9 shoe.  You can’t order a TV screen by the inch.

X. Does metrication mean we have to drive on the right and adopt the Euro?

  • These are completely separate issues, and UKMA takes no view on them.
  • Changing to driving on the right would be expensive and is unnecessary.
  • One third of the world’s population drives on the left, including Japan, India and South Africa.
  • In 1970, Burma, also known as Myanmar, switched from driving on the left to driving on the right. However, it is one of the few countries that retains imperial measurements for most purposes.
  • Sweden switched from driving on the left to driving on the right in 1967, but did not join the EU until 1995, and is not in the Eurozone.
  • Cyprus, Malta and the Republic of Ireland use the Euro and have metric road traffic signs, but drive on the left.
  • Over a third of EU states have opted out of the Euro.

Y. Metrication is undemocratic.  It was imposed without consultation and has never been debated in Parliament or included in any election manifesto.

  • Metrication was announced to Parliament in 1965 in response to a request by British industry.
  • Every stage of metrication has been approved as either primary or secondary legislation and laid before both Houses of Parliament for approval.  There have been several debates in both Houses, e.g. on 18 October 1976 when the Weights and Measures Act5 was given a second reading in the House of Commons.  The most recent was on 14 March 2001 when the Weights and Measures (Metrication Amendments) Regulations6 were approved by 263 votes to 182.

Z. The metric system is itself a muddle.  Supporters of metric argue about whether to use millimetres or centimetres (and millilitres or centilitres).

  • There is no muddle.  All these units are valid metric units.  There is a choice of multiples and subdivisions, depending on the convenient size of numbers resulting.
  • However, millimetres are recommended for exclusive use in technical drawings and specifications.  This is to remove any possible confusion and also to avoid or reduce the need for decimal points.

4 See OECD (2010), PISA 2009 Results: Executive Summary, available online at

5 See

6 See