UK Metrication timeline

Date Event
1668-04-13 John Wilkins proposes a universal decimal system of measurement, which includes the core elements of the future metric system. In An Essay Towards a Real Character, And a Philosophical Language, published by the Royal Society, he proposes a universal standard of length, based on either a fraction of a meridian of the Earth, or the length of a pendulum with a period of one second. A standard unit of weight would be defined by the weight of distilled water in a cube with sides equal in length to the universal standard of length.
1790-04-13 Sir John Riggs Miller and the Bishop of Autun, Prince Talleyrand put, to the British Parliament and French Assembly respectively, the proposition that the two countries should cooperate to equalise their weights and measures, by the joint introduction of the metric system.
1819       First Report of the Commissioners appointed to consider more Uniform Weights and Measures: “A general uniformity of Weights and Measures is so obviously desirable in every commercial country, in order to the saving of time, the preventing of mistakes, and the avoiding of litigation”. The report recommends a new standard gallon defined by the volume occupied by 10 pounds of water.
1834-10-16 The standard pound and the standard yard are destroyed when the Houses of Parliament burn down.
1849 The first step to a decimal currency is taken, with the introduction of the florin, which had a value of 1⁄10 pound, or two shillings.
1862-07-15 The Report from the Select Committee on Weights and Measures recommends that the use of the metric system be rendered legal.
1879-01-01 The Troy pound and the pennyweight cease to be legal for trade.
1895-07-01 The Report from the Select Committee on Weights and Measures recommends that the metric system be legalised for all purposes, and be rendered compulsory by 1897.
1907 The Met Office adopts the millibar for the measurement of upper-air pressure.
1908 The Olympic Games are held in London. All track and field events are in metric units.
1914-05-01 The Met Office adopts the millimetre for rainfall measurement, the millibar for surface air pressure, and the metre per second for wind speed.
1946 The Commonwealth Science Congress recommends a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth.
1950-12 The Hodgson Report of the Committee on Weights and Measures Legislation recommends that the Government should take steps, in concert with the Commonwealth and USA, to abolish the Imperial system of measurement and replace it by the metric system over a period of 20 years.
1959 With support from the British Standards Institution, the UK adopts metric paper sizes. Described in ISO 216, the A-series of paper sizes are based on a rectangle with an area of 1 m2.
1959-07-15 The Post Office adopts the metric-based “A” series of paper sizes, beginning with A4 for headed note paper. The related metric-based “B” and “C” series of paper sizes are also adopted for new standard envelope sizes.
1961-01-01 The Met Office switches internally from degrees Fahrenheit to degrees Celsius.
1962-10-15 The degree Celsius becomes the primary unit in all public weather forecasts issued by the Met Office.
1964-01-31 New metric definitions for the yard and pound come into effect:
1 yard = 0.9144 m, 1 pound = 0.453 592 37 kg.
1965-05-24 The Government announces its intention that within 10 years the greater part of the country’s industry should have changed to the metric system.
1966-03 The British Standards Institution publishes Metric Standards for Engineering, a guide book for engineering firms planning the switch to metric manufacturing.
1966-03 The Parliamentary Standing Joint Committee on Metrication is appointed.
1967-01-01 The Met Office adopts the metric system for all references to height and distance, including centimetres for snowfall measurement, and metres and kilometres for the measurement of visibility.
1967 Metrication in the construction industry begins. The Ministry of Public Building and Works publishes a leaflet entitled Going Metric in the Construction Industry.
1967-05 At a meeting of German, French and UK government representatives, supported by standards representatives from DNA, AFNOR and BSI, it is agreed to recommend that the calorie should be replaced by the joule by January 1978.
1968-01-01 The Ministry of Housing and Local Government and the Welsh Office, issues a Joint Circular announcing the first stage of the change to the metric system in the construction industry.
1968-01 The Royal Society publishes Metrication in Scientific Journals, recommending the adoption of SI in all scientific and technical journals as quickly as possible.
1968-03-20 The Royal Society recommends that in primary schools there should be a change of emphasis in favour of the metric system from September 1969, and that SI units should be exclusively used in GCE and CSE maths exams not later than 1972.
1968-04-23 The first two decimal coins are introduced – the 5p and 10p coins. They are used as coins equivalent to one shilling and two shillings until decimalisation in 1971.
1968-07-26 The Government announces that the target date for the completion of the metrication programme is 1975.
1968-11-08 The UK signs the Vienna Convention on Road Signs and Signals. The Convention prescribes restriction signs with vehicle dimensions shown in metres only.
1969 Knitting yarns in round metric pack sizes are introduced.
1969 The Ordnance Survey begin a metrication programme, with plans to replace the 1:10 560 scale with 1:10 000, for 1-inch to 1-mile maps to be replaced with a new 1:50 000 map series, and for all contours and altitudes to be expressed in metric units.
1969-02 The Royal Society sets up a working party to consider the adoption of the joule as the unit of energy in nutritional sciences. It is agreed that the calorie should fall into disuse and the joule be adopted as the unity for energy in all nutritional work.
1969-03-03 The metric system becomes obligatory for the dispensing of all prescriptions. Bottled medicines are accompanied by 5 mL spoons.
1969-03-05 The Government announces that speed limits will go metric in 1973.
1969-05-28 The UK Metrication Board holds its first meeting under the chairmanship of scientist and broadcaster Lord Ritchie-Calder.
1969-09 The Royal Society publishes two pamphlets for teachers concerning the introduction of the metric system: Metric Units in Primary Schools and Metrication in Secondary Education.
1970-01-01 The British Non-Ferrous Metals Federation switches to the metric system for product specification, and decimal currency for pricing.
1970-01-01 Electic wiring goes metric. Wiring is now measured in cross-sectional area e.g. The old 5-A wire becomes 1 mm2.
1970-01 Bricks supplied in metric sizes. Wire rods supplied in metric sizes.
1970-01 Softwood imported in metric sizes.
1970-01-30 British Standards Institution issues BS 3921 – the new metric British standard on bricks.
1970-04 Plasterboard supplied in metric sizes.
1970-04-01 Paving slabs supplied in metric sizes.
1970-04-01 Sawn softwood sold in metric sizes.
1970-06-17 The first three decimal postage stamps are introduced – the 10p, 20p and 50p stamps. They are used as stamps equivalent to two, four and ten shillings until decimalisation in 1971.
1970-06 City and Guilds exams in construction based on SI units.
1970-07 The Commonwealth Games adopts metric units for all events. For example, in athletics, the 100 m replaces the 100 yards.
1970-08 Dunlop publishes two booklets, Metrication and the Dunlop Company and Think Metric, as part of its switch to the metric system.
1970-08 Wire sizes go metric.
1970-09-28 Pilkingtons switch to metric measurements and decimal currency for all flat glass and fibreglass products.
1970-10 Metrication of flat glass completion (planned).
1970-12-09 The Government announces that speed limits will now not be made metric in 1973, and “have no alternative date in mind”.
1971 Beds in metric sizes introduced.
1971 Knitting patterns include body measurements in centimetres as well as inches.
1971-01-01 Apothecaries’ weights and measures cease to be legal for trade.
1971-01-01 Lead sheet and lead pipe supplied in metric sizes.
1971-01-01 Aluminium windows supplied in standard metric sizes. Imperial sizes only supplied as special orders.
1971-01-01 Imported hardwood trade switches to metric for stock-keeping and sales.
1971-01-01 Sand and gravel goes metric.
1971-02-15 Decimal Day (D-Day). Thorough planning, and an extensive public information campaign, ensures a smooth changeover to decimal money.
1971-07 Paint in metric sizes becomes available. The paint industry completes the switch to metric in 1972.
1971-08-31 Asbestos cement corrugated sheets switch to metric sizes.
1971-07-01 Steel fabric reinforcement manufacturers go metric.
1972-01-01 UK port authorities introduce metric units as the basis for their freight charges.
1972-01 Roofing felt and damp-proof courses manufactured to metric measurements only.
1972-02 The Government publishes its White Paper on Metrication. Amongst other things, this initiates metrication in the food sector.
1972-04 British Steel switches to metric. Steel is sold in tonnes, with dimensions for most products in metric units.
1972-09 The Royal Society supports the use of the joule instead of the calorie for food energy, and recommends that terms such as “calorie intake” be replaced with “energy intake”.
1974 The Distributive Industry Training Board (DITB) publishes The Metric Shop, a guide to metric changes and training in shops.
1974 Metrication of clothing begins. Clothes such as men’s shirts are required to be labelled in metric units in addition to traditional imperial measures. Imperial units are initially planned to be phased out by the end of 1975.
1974-07-01 Prescribed metric pack sizes are introduced for pasta.
1974 Blankets switch to metric sizing from Autumn 1974.
1975 The International Rugby Football Board switches to metric for all measurements. The 25-yard line becomes the 22-metre line.
1975-01-01 Prescribed metric pack sizes are introduced for salt.
1975-02 Retailers of fabrics and carpets start selling in metric on a voluntary basis.
1975-05-05 British Rail traffic switches to kilograms and tonnes for load capacities and braking force.
1975-07 Agriculture and horticulture switch to metric over a period of 18 months.
1975-09-29 The Post Office switches to grams and kilograms for all postal tariffs.
1975-10-01 Prescribed metric pack sizes are introduced for sugar.
1975-11-01 Prescribed metric pack sizes are introduced for breakfast cereals.
1976 The imperial gallon is redefined as 4.546 09 dm3. Bulk sales of petroleum go metric.
1976 A defence standard is developed prescribing the metric units to be used by the Ministry of Defence, including the services.
1976 Knitting needles switch to millimetres for diameters. The old SWG-based size numbers are phased out.
1976-02 The Annual Farm Review is published in metric.
1976-04 Milk wholesale sales and official production statistics in Scotland switch to litres.
1976-06-04 Returns for the Agricultural Census are completed in metric units for the first time.
1976-10 Milk wholesale sales and official production statistics in England, Wales and N.Ireland switch to litres.
1976-12 Agriculture, horticulture and allied industries essentially metric by year-end.
1977 Livestock auctions and deadweight markets switch to metric trading.
1977-01-01 Speedometers in all new vehicles are required to be marked in both km/h and mph.
1977-01-01 Prescribed metric pack sizes are introduced for butter, margarine and other edible fats.
1977-01-01 Prescribed metric pack sizes are introduced for dried fruits e.g. raisins, sultanas, dates.
1977-07-01 Prescribed metric pack sizes are introduced for flour. e.g. 1.5 kg replaces 3 lb.
1978 Solid fuel retailing goes metric.
1978-01-01 Chocolate bars of 85 g or more are required to be sold in prescribed metric sizes.
1978-01-01 All packaged goods, that are required to be marked with quantity by measurement, must be marked in metric and imperial units. Imperial-only quantity markings on pre-packed foods, and most other goods, comes to an end.
1978-01-01 Prescribed metric pack sizes are introduced for biscuits and shortbread.
1978-01-01 Prescribed metric sizes are introduced for bread. e.g. 400 g, 800 g.
1978-04-01 Prescribed metric pack sizes are introduced for tea and tea bags.
1978-04-27 The chain, furlong, nautical mile, rood, cubic yard, bushel, dram, and cental cease to be legal for trade.
1978-05-02 Bread completes the switch to metric sizes. e.g. 400 g replaces 14 oz.
1978-05-15 Wine prepacked in quantities between 50 ml and 5 L is bottled only in a standard range of metric sizes, e.g. 375 ml, 500 ml, 750 ml (75 cl) and 1 L.
1978-09-01 Cocoa powder is required to be sold in prescribed metric sizes.
1979 London commodity market completes change to metric.
1979-06 Manufacturers of tobacco products voluntarily switch to marketing all pre-packed pipe and hand-rolling tobacco in metric quantities only.
1979-07-01 Prescribed metric pack sizes are introduced for instant coffee.
1979-08-27 Pre-packed margarine and butter complete the switch to metric sizes. e.g. 500 g replaces 1 lb.
1979-11-14 Minister for Consumer Affairs, Sally Oppenheim, announces the abolition of the Metrication Board.
1980-01-01 All packaged goods, that are required to be marked with quantity by measurement, must be marked in metric units.
1980-01-01 Prescribed metric sizes are introduced for pre-packed milk. Milk becomes available in one-litre plastic cartons in supermarkets.
1980-04-30 The Metrication Board is abolished.
1980-06-30 Tea and tea bags complete the switch to metric pack sizes. e.g. 125 g replaces 4 oz.
1980-09-01 The hand, square inch, square mile, cubic inch, cubic foot, cran, grain, stone, quarter, hundredweight and ton cease to be legal for trade.
1981 Pricing per litre is permitted at petrol stations.
1982-01-01 Prescribed metric pack sizes are introduced for ground coffee and coffee beans.
1982-01-01 Prescribed metric pack sizes are introduced for rice, cereal grains and starches.
1990-01-01 Prescribed metric pack sizes for knitting yarns are introduced. The legislation has little practical effect, as pack sizes have been metric since the early 1970s.
1994 All petrol pumps are required to be calibrated in litres.
1995 The Report by the Department of Trade and Industry on Metrication notes that consumer groups consider that delaying still further the completion of metrication would not be in the best interest of consumers.
1995-01-01 All spirits in pubs are served exclusively in metric quantities of 25 mL or 35 mL.
1995-10-01 The gill ceases to be authorised for all official purposes.
1995-10 Goods sold by quantity, including food pre-packed in variable weights such as cheese and meats, are required to be traded in metric units.
2000 The therm, and fathom, cease to be authorised for all official purposes.
2000-01-01 Loose goods sold by weight, volume or length must be priced and measured using metric units.
2002 The UK Metric Association (UKMA) is formed – an independent, non-party political, single issue organisation advocating the full adoption of the metric system for all official purposes in the United Kingdom as soon as practicable.
2003 Driver location signs are introduced on motorways and major highways. These show road locations in kilometres, to one decimal place. They augment, in a more driver-visible form, the information already shown on distance marker posts used by highway engineers since the 1960s.
2004-07-22 The Price Marking Order 2004 comes into effect. Shops with a floor area greater than 280 m2 are required to display metric unit pricing for packaged goods.
2007-09-28 The Highway Code includes km/h equivalents for all speed limits for the first time.
2008-01-01 All goods vehicles over 3.5 t, and buses with more than 8 passenger seats, registered since 2005 are required to be fitted with a speed limiter to restrict the maximum powered speed to 90 km/h for goods vehicles, and 100 km/h for buses.
2008-08 A LACORS report recommends that all scales used for medical applications should display metric units only: “One of the most potentially harmful issues is that of switchable scales – those that can display metric, imperial and other units. The risk is that medication could be administered based on a readout that was assumed to be metric.”
2009-10 The Department for Transport proposes giving local authorities the option of showing cycle journey times, in place of miles, on cycle route distance signs. The proposal creates a mix of different units on signs across the National Cycle Network.
2009-10 The Department for Transport announces its intention to end the use of imperial-only width and height restriction signs on Britain’s roads. The plan is later cancelled by the Secretary of State for Transport.
2010-01-01 The acre ceases to be authorised for all official purposes.
2015-04-06 In England and Wales, the speed limit on dual carriageways for HGVs over 7.5 t is increased from 50 mph to 60 mph (96 km/h), raising it above the 90 km/h setting of HGV speed limiters.
2016-04-22 All new vehicle restriction signs on public highways are required to show both metric and imperial units. Dual unit restriction signs had been optional since 1981. No termination date is set for remaining imperial-only signs.
2020 During the COVID-19 pandemic, social distancing legislation and official guidance is given exclusively in metric. In public places people are asked to keep at least 2 metres apart.
2020-05-09 The Department for Transport issues traffic signs for COVID-19, with exclusively metric units for pedestrian social distancing signage.
2020-06-13 New definitions for the SI base units come into effect in Weights and Measures legislation.
2020-07-04 Legislation for e-scooter trials comes into effect. Requirements include a maximum design speed not exceeding 15.5 mph. This renders illegal the use of e-scooters with 25 km/h (15.53 mph) speed limiters.
2022-06-03 The Government announces the return of imperial units with a public consultation on the Choice on Units of Measurement: Markings and Sales. The proposal is presented as a fait accompli. Respondents are invited to choose whether traders, choosing to sell items in imperial units in the future, should be required to show a metric equivalent alongside the imperial or not. No option is offered to keep the 22-year long status quo of metric-only. The Government links the return of imperial measures to the Queen’s Platinum Jubilee celebrations. If enacted, it would be the first major regression in metrication since 1812, when Napolean temporarily abandoned the metric system in France for Mesures usuelles.
20??-??-?? TO BE ARRANGED – The day that road speed limits switch from mph to km/h (originally planned for 1973, but put on hold in December 1970).