Does the UK Use Metric or Imperial? The UK Measurement System Explained
Quick answer: The UK uses both. Metric is the legal primary system for trade, packaging, science, healthcare and most official records, while imperial units remain lawful for road signs in miles and yards, pints of draught beer and cider, milk in returnable bottles and the troy ounce for precious metals. Informally, many people still think in stones, feet and miles.
This section explains what the law actually requires, where each system turns up in everyday British life, what changed after the 2022 consultation on imperial units, and how to move between the two without mistakes.
Is the UK officially metric?
Yes, for most legal purposes the UK is a metric country. Goods sold by quantity must be measured and labelled in metric units, and metric is the system used in schools, hospitals, science, engineering and government statistics. Imperial units have not disappeared, though. They are defined in metric terms, they can still appear next to metric figures, and a handful of uses keep imperial as the main unit.
How did Britain end up with two systems?
The UK moved to metric gradually over several decades rather than in one switch-over. The imperial system was standardised across the country by the Weights and Measures Act 1824. In the twentieth century, trade with metric countries pushed industry and government towards the metric system, but the change was introduced sector by sector.
- 1963: the Weights and Measures Act 1963 defined the yard and the pound in metric terms (0.9144 metres and 0.45359237 kilograms), so imperial units have been legally tied to metric ones ever since.
- 1965: the government backed a move to metric, and a Metrication Board coordinated it from 1969 until 1980.
- 1985: the Weights and Measures Act 1985 became the main law on units for trade in Great Britain, with the Units of Measurement Regulations 1986 listing the units that may be used.
- 1995 and 2000: metric became compulsory for most packaged goods in 1995, then for loose goods sold by weight, such as fruit on a market stall, from 1 January 2000.
- 2023 and 2024: after a public consultation the government kept the metric rules unchanged, and wine became available in a new 568 ml “pint” bottle size.
What does UK law say about metric and imperial units?
Metric units must be the primary indication for trade, and imperial units are allowed only as an extra, less prominent figure. In Great Britain the main statute is the Weights and Measures Act 1985. Northern Ireland has the equivalent Weights and Measures (Northern Ireland) Order 1981, and the Units of Measurement Regulations 1986 apply across the whole UK. Together they decide which units a trader may use when selling by length, weight, volume or area.
Government guidance published with the consultation outcome in December 2023 restates the key rule. Imperial “supplementary indications” are lawful alongside metric, but the imperial figure must be less prominent and printed in characters no larger than the metric one. A pack of cheese can therefore say “400 g (14.1 oz)”, but it cannot say “14 oz” on its own.
These rules apply to trade only. Nobody is stopped from using feet, stones or pints in conversation, in a family recipe or in a fitness log.
Where can imperial units still be the main unit?
Imperial units can still be the main unit for a short list of specific uses. Outside these, imperial can only be a secondary figure next to the metric one.
- Pint: draught beer and cider served in pubs and bars, and milk sold in returnable containers, such as glass bottles delivered to the doorstep.
- Troy ounce: transactions in gold, silver and other precious metals. One troy ounce is 31.1034768 grams, heavier than the ordinary 28.35 g ounce.
- Mile, yard, foot and inch: road traffic signs and the related measurement of distance and speed, which is why speed limits are in miles per hour and direction signs give distances in miles and yards.
Pub measures are fixed by law as well. Draught beer and cider must be sold as a third, a half or two-thirds of a pint, or in multiples of half a pint. Gin, rum, vodka and whisky are sold in 25 ml or 35 ml measures (a venue picks one, not both), and still wine by the glass comes in 125 ml or 175 ml, or multiples of those.
What happened after the 2022 imperial units consultation?
The law did not change: the government kept metric as the primary system. The consultation, titled “Choice on units of measurement: markings and sales”, ran from 3 June to 26 August 2022 and asked whether businesses should be free to sell in imperial units without a metric equivalent. It received 101,108 responses.
The government published its response on 27 December 2023. It reported that most respondents had limited or no appetite for greater use of imperial measures, and it kept the existing rules: metric first, with imperial allowed as a supplementary figure. On the same day it announced new permitted wine bottle sizes, including a 568 ml “pint” for still and sparkling wine, which reached shops in 2024.
Which units do people in the UK use day to day?
Most official and commercial measurements are metric, but personal measurements are often imperial. The quick-reference chart below shows what you are likely to see in common situations. The second column is the unit used on labels, forms and signs; the third is how people often talk.
| Situation | Usual official unit | Everyday usage | Example |
|---|---|---|---|
| Road distance and speed | Miles, yards, mph | Miles, mph | 30 mph limit; exit in 1 mile |
| Fuel at the pump | Litres | Litres, with economy in miles per gallon | 50 litres; 50 mpg |
| Draught beer and cider | Pint and fractions of a pint | Pint, half | 1 pint = 568 ml |
| Milk in shops | Litres, often with pints alongside | Pints | 4 pints = 2.27 litres |
| Packaged food | Grams and kilograms | Grams; older recipes in ounces | 500 g (1.1 lb) |
| Body weight | Kilograms in NHS records | Stones and pounds | 70 kg = about 11 st |
| Height | Centimetres in medical records | Feet and inches | 178 cm = about 5 ft 10 in |
| Weather temperature | Degrees Celsius | Celsius; some still quote Fahrenheit | 20°C = 68°F |
| Building and DIY | Millimetres and metres | Millimetres, with some inch-based names | 2.4 m plasterboard sheet |
| TV and phone screens | Inches in product names | Inches | 55-inch TV = 139.7 cm diagonal |
| Property floor area | Square metres, often with square feet | Square feet | 80 m² = 861 ft² |
| Precious metals | Troy ounce | Troy ounce, grams | 1 troy oz = 31.1 g |
Why do people in Britain still use stones, feet and miles?
Habit, road signs and a long, partial changeover keep imperial units familiar. Anyone who went to school before the 1970s learned imperial units first, and many households passed those habits on. Road signs never switched to kilometres, so miles remain the natural unit for journeys, and pub culture keeps the pint alive.
Body measurements show the split most clearly. Bathroom scales usually display both kilograms and stones, GP and hospital records use kilograms and centimetres, yet people commonly describe their weight as “11 stone 4” and their height as “five foot ten”. The national curriculum in England reflects this mix: pupils are taught metric units, and in Year 5 they also learn approximate equivalences between metric units and common imperial units such as inches, pounds and pints.
What are the exact metric equivalents of imperial units?
Every imperial unit has an exact metric definition, so conversions never need to be guesses. One inch is exactly 2.54 centimetres and one pound is exactly 0.45359237 kilograms; most other units follow from these two. The chart below lists the factors used across this site.
| Imperial unit | Metric equivalent | Handy approximation |
|---|---|---|
| 1 inch (in) | 2.54 cm exactly | 2.5 cm |
| 1 foot (ft) = 12 in | 30.48 cm exactly | 30 cm |
| 1 yard (yd) = 3 ft | 0.9144 m exactly | 0.9 m |
| 1 mile = 1,760 yd | 1.609344 km exactly | 1.6 km |
| 1 ounce (oz) | 28.349523125 g | 28 g |
| 1 pound (lb) = 16 oz | 0.45359237 kg exactly | 450 g |
| 1 stone (st) = 14 lb | 6.35029318 kg | 6.35 kg |
| 1 UK pint | 568.26125 ml | 570 ml |
| 1 UK gallon = 8 pints | 4.54609 litres | 4.5 litres |
| 1 acre | 4,046.86 m² | 0.4 hectares |
How should you write measurements in the UK?
Lead with the metric value and add imperial in brackets if your reader needs it. This mirrors how labels are required to work and how most UK publications handle units. A few simple conventions make figures easier to read:
- Leave a space between the number and the symbol: 25 cm, 2 kg, 500 ml.
- Symbols never take an “s”: write 5 km and 10 kg, not 5 kms or 10 kgs.
- Give temperatures in degrees Celsius first, with Fahrenheit in brackets only if needed.
For precise answers, the site’s length converter, weight converter and volume converter all use the exact definitions above, so you can check any figure on a label or form.
Guides and converters in this section
New guides on UK measurement law and everyday use appear in the list further down as they are published. These converters handle the metric and imperial switches people make most often.
Distance and height
- Miles to km converter: turn road distances and running routes into kilometres.
- Km to miles converter: useful for race distances.
- Feet to cm converter: convert a height in feet and inches into centimetres for forms.
Weight, volume and temperature
- Kg to lb converter and lb to kg converter: switch between the units on scales and labels.
- Litres to gallons converter: compare fuel and tank capacities in UK gallons.
- Celsius to Fahrenheit converter: translate weather and oven temperatures.
Latest UK measurement system guides
- UK vs US Cup Measurement: How Many ml Is a Cup?
- UK vs US Pint Difference: 568 ml vs 473 ml Explained
- UK vs US Gallon Difference: Converter and Chart
- Which Imperial Units Are Still Legal in the UK?
- Pint of Beer Size UK: How Many ml in a Pint?
- Is It Legal to Sell in Pounds and Ounces in the UK?
- Weights and Measures Act 1985 Explained: A UK Guide
- When Did the UK Go Metric? Key Dates from 1965 to 2000
- Why Does the UK Use Stone for Weight? A 14 lb History
- Why Does the UK Still Use Miles? The History and the Law
Related sections
For the bigger picture on SI, metric and imperial units, start with the units of measurement guide. For worked conversions, see length and distance conversions, weight conversions in stones, pounds and kilograms and volume conversions for pints, litres and gallons.
Frequently asked questions
Is the UK metric or imperial?
The UK is officially metric for trade, packaging, science and healthcare, but imperial units are still used on road signs, for draught beer and cider, for milk in returnable bottles and for precious metals. Many people also use imperial units informally for height and body weight.
Is it legal to sell food in pounds and ounces in the UK?
Only as a supplementary indication. Goods sold by weight must be priced and labelled in metric units, and an imperial figure can be shown alongside as long as it is less prominent and no larger than the metric one.
Why are UK road signs in miles?
The Units of Measurement Regulations allow the mile, yard, foot and inch for road traffic signs and the related measurement of distance and speed, and British road signs were never converted to kilometres. Speed limits are therefore set in miles per hour.
Did the 2022 consultation bring back imperial units?
No. The government published its response on 27 December 2023 and kept the existing law, with metric as the primary unit and imperial allowed as a supplementary figure. Separately, still and sparkling wine can now be sold in 568 ml pint bottles.
Sources
- Weights and Measures Act 1985, legislation.gov.uk
- Units of Measurement Regulations 1986, legislation.gov.uk
- Choice on units of measurement: markings and sales, consultation and outcome, GOV.UK
- Weights and measures: the law, GOV.UK
- Pints of wine stocked on Britain’s shelves for the first time ever, GOV.UK news, 27 December 2023
- National curriculum in England: mathematics programmes of study, Department for Education
- The International System of Units (SI Brochure), BIPM