Quick answer: The UK still uses miles because road signs, distances and speed limits were deliberately left out of metrication. The law expressly permits the mile, yard, foot and inch on traffic signs and for speed and distance, and successive governments since 1970 have chosen not to convert them, citing cost and safety. One mile is 1.609344 km.
Britain has sold its groceries in grams and its petrol in litres for decades, yet every motorway sign still counts down in miles and every speed camera enforces miles per hour. That split is not an oversight; it is written into law. This explainer covers the legal position, the history behind it and what a switch to kilometres would involve. For the wider picture of where metric and imperial units each apply, see our guide to how the UK measurement system works.
Is it legal for the UK to use miles?
Yes. Miles are lawful on UK roads because road signs are governed by traffic law, not trading law. The Traffic Signs Regulations and General Directions 2016 prescribe the signs highway authorities in Great Britain may put up, and those signs give distances in miles and yards and speed limits in miles per hour.
Trading law treats the mile differently. The Weights and Measures Act 1985 places it in Part VI of Schedule 1, a list headed “units which may not be used for trade except as supplementary indications”. In other words, a business cannot sell something priced purely by the mile, but a highway authority can sign a junction as one mile ahead. That division explains why the mile thrives in public life while the yard of fabric has largely given way to the metre at the shop counter.
While the UK was in the European Union, the relevant directive (80/181/EEC, as amended) gave the UK and Ireland a specific exemption to keep the mile, yard, foot and inch for road traffic signs and for distance and speed measurement. Since Brexit the choice rests entirely with UK governments, and the mile has stayed.
Why did miles survive when other units went metric?
Roads were scheduled to convert, but the plan was shelved in 1970 and never revived. Britain’s metric programme began with a written parliamentary answer on 24 May 1965, which said industry should adopt metric units “sector by sector” with most of the change made within ten years. It was a voluntary, gradual approach rather than a single switchover day.
Converting speed limit signs to kilometres per hour was pencilled in for 1973. In December 1970 the government announced that the change would not go ahead and set no alternative date. Government papers from the time, summarised by the UK Metric Association, show ministers felt the public already had enough to absorb with decimal currency, which arrived on 15 February 1971, and that compulsory conversion sat awkwardly with a voluntary metric policy.
The Metrication Board, set up in 1969 to steer the switch, was wound up in 1980. Later metric requirements were driven mainly by rules on units used in trade: packaged goods went metric from 1 October 1995 and loose foods from 1 January 2000. Road signs involve no buying or selling, and the exemption for them was never withdrawn, so the mile simply carried on.
Where does the mile come from?
The mile started as the Roman mille passus, a thousand double paces of roughly 1,480 metres. English miles varied from region to region for centuries until an Act of Parliament in 1593, under Elizabeth I, fixed the statute mile at eight furlongs, with the rod set at 16½ feet. That gives 5,280 feet, or 1,760 yards.
The mile’s exact metric length came much later. In 1959 the UK, the United States and other English-speaking countries agreed common definitions of the yard and the pound, and UK law now defines the yard as exactly 0.9144 metres. Multiply by 1,760 and one mile equals exactly 1,609.344 metres.
| Unit | In yards | In feet | Metric equivalent |
|---|---|---|---|
| Chain | 22 yd | 66 ft | 20.1168 m |
| Furlong (10 chains) | 220 yd | 660 ft | 201.168 m |
| Mile (8 furlongs) | 1,760 yd | 5,280 ft | 1,609.344 m |
The chain and furlong sound archaic, but both survive: horse races in Britain are still run over distances in furlongs, and railway engineers locate points on the track in miles and chains. To convert distances quickly, use the miles to km converter.
What would switching to kilometres involve?
Every distance and speed limit sign would need changing, along with the laws that set the limits. Speed limits are written into legislation and local traffic orders in miles per hour, so a switch would mean amending those rules, replacing or covering hundreds of thousands of signs, and updating enforcement equipment and driver training material.
Cost is the reason most often given for leaving things alone, and the estimates vary wildly. The 1970 planning papers put the cost of converting speed limit signs at a few million pounds in the money of the day, while a Department for Transport estimate in 2006 ran to hundreds of millions. Campaigners on both sides dispute the figures. What nobody disputes is that a period of mixed mph and km/h signs would need careful handling for road safety.
Ireland shows that the change is possible. Its direction signs moved to kilometres from the 1970s, and speed limits switched from mph to km/h on 20 January 2005, backed by a public awareness campaign. Since then, anyone driving from Northern Ireland into the Republic changes units as well as jurisdiction at the border.
What are UK speed limits in km/h?
The common UK speed limits of 20, 30, 40, 50, 60 and 70 mph equal roughly 32, 48, 64, 80, 97 and 113 km/h. These are exact conversions using 1 mile = 1.609344 km, rounded to one decimal place. Countries that use km/h normally set limits in round tens, so a converted UK system would probably not keep these exact values.
| Limit (mph) | Exact equivalent (km/h) | Where you typically see it |
|---|---|---|
| 20 mph | 32.2 km/h | Many residential streets; the default on most restricted roads in Wales |
| 30 mph | 48.3 km/h | Built-up areas with street lighting in England and Scotland |
| 40 mph | 64.4 km/h | Busier urban and suburban roads |
| 50 mph | 80.5 km/h | Some rural A roads and roadworks |
| 60 mph | 96.6 km/h | National speed limit for cars on single carriageways |
| 70 mph | 112.7 km/h | National speed limit for cars on dual carriageways and motorways |
For any other speed, the speed converter handles mph, km/h, metres per second and knots.
Where else are miles still used in the UK?
Outside road signs, miles live on in speech, sport, rail and motoring. Most people in Britain still give journey lengths in miles even if they buy fabric by the metre, and several institutions keep the unit in daily use:
- Running: the marathon is 26.2 miles (42.195 km), while parkrun events are a metric 5 km.
- Railways: track positions on the British network are recorded in miles and chains, and lineside mileposts mark them.
- Motoring: fuel economy is usually quoted in miles per gallon, even though fuel has been sold by the litre since the 1990s.
- Walking: Ordnance Survey maps use a metric grid of 1 km squares, yet route guides commonly give walk lengths in miles.
- At sea and in the air: the nautical mile is a different unit altogether, defined as exactly 1,852 metres.
One kilometre equals 0.621 miles, so a 10 km race is about 6.2 miles. The km to miles converter covers the reverse direction.
Do any other countries still use miles?
The United States is the other large country whose roads are signed in miles. A handful of smaller places with British or American links also use them. Most of the Commonwealth went the other way: Australia and Canada, for example, converted their road signs to kilometres in the 1970s.
Will the UK ever switch to kilometres?
No government has announced plans to convert UK road signs to kilometres. The government’s 2022 consultation on units of measurement dealt with how goods are marked and sold, not with roads, and its December 2023 response left the existing law in place.
There has been one small metric step on the roads. Since the 2016 sign regulations took effect, new height and width limit signs must show metric values alongside feet and inches, partly because vehicle dimensions are usually given in metres. A low bridge signed 14′6″ (4.42 m) will now typically also show 4.4 m. Speed and distance, though, remain firmly imperial. For the full list of units that have survived, the units of measurement guide sets out both systems side by side.
Frequently asked questions
Can UK road signs show kilometres?
Not for distances or speed limits. Official signs in Great Britain must follow the Traffic Signs Regulations and General Directions 2016, which use miles, yards and miles per hour. New height and width limit signs, however, must show metres alongside feet and inches.
How many kilometres are in a mile?
One mile is exactly 1.609344 kilometres. For a quick mental estimate, multiply miles by 1.6, or remember that 5 miles is almost exactly 8 km.
Why is a mile 5,280 feet?
An Act of Parliament in 1593 fixed the statute mile at eight furlongs. A furlong is 40 rods of 16.5 feet, or 660 feet, and eight times 660 is 5,280.
When did Ireland switch to kilometres per hour?
The Republic of Ireland changed its speed limits from mph to km/h on 20 January 2005. Its direction signs had already been showing distances in kilometres since the 1970s.
Can a UK business sell things by the mile?
Only as a supplementary indication. The Weights and Measures Act 1985 lists the mile among units that may not be used for trade except alongside a metric figure, which must be the more prominent of the two.
Sources
- Weights and Measures Act 1985, Schedule 1 (legislation.gov.uk)
- The Traffic Signs Regulations and General Directions 2016 (legislation.gov.uk)
- Know your traffic signs, Department for Transport
- Choice on units of measurement: consultation response, Department for Business and Trade, December 2023
- Why the government scrapped plans to convert speed limit signs in 1970, Metric Views (UK Metric Association, a pro-metric campaign group, drawing on National Archives papers)
- Metric speed limit awareness campaign launched, RTÉ News, January 2005