Length and Distance Conversions (UK Guide)
Quick answer: Length conversions between imperial and metric units use exact factors: 1 inch is 2.54 cm, 1 foot is 30.48 cm, 1 yard is 0.9144 m and 1 mile is 1.609344 km. Multiply by these to go from imperial to metric, and divide to go back. Metric is standard in the UK, but miles stay on road signs.
This section covers everyday length and distance conversions for UK readers, from millimetres on a tape measure to miles on a road sign, with charts, worked examples and the mistakes that catch people out.
Which length units are used in the UK?
The UK uses metric units for almost all official and technical lengths, with imperial units surviving in a few familiar places. Millimetres are the working unit for building, joinery and engineering drawings, centimetres for clothing and body measurements, metres for rooms and gardens, and kilometres for running events and maps. Ordnance Survey maps, for example, use a kilometre grid.
Imperial lengths are still the default in conversation and in a few protected uses. Road signs give distances in miles and yards and speed limits in miles per hour, most people describe their height in feet and inches, and televisions and phone screens are sold by their diagonal in inches. Sport keeps older units too: a cricket pitch is 22 yards (20.12 m) between the wickets, golf courses are measured in yards and horse races in furlongs.
For background on why both systems coexist, see the guide to the UK measurement system and the law. For any value not covered on this page, the length converter handles every common unit.
What are the most useful length conversion factors?
The factors below cover nearly every everyday length conversion. Factors marked “exact” come straight from the definitions of the inch, yard and mile, which have been fixed in metric terms since the international yard was agreed in 1959. The others are rounded to four significant figures, which is more than enough for home use.
| To convert | Into | Multiply by | Example |
|---|---|---|---|
| Millimetres | Inches | 0.03937 | 100 mm = 3.94 in |
| Centimetres | Inches | 0.3937 | 30 cm = 11.81 in |
| Inches | Centimetres | 2.54 (exact) | 12 in = 30.48 cm |
| Feet | Centimetres | 30.48 (exact) | 6 ft = 182.88 cm |
| Feet | Metres | 0.3048 (exact) | 10 ft = 3.048 m |
| Metres | Feet | 3.281 | 3 m = 9.84 ft |
| Yards | Metres | 0.9144 (exact) | 100 yd = 91.44 m |
| Metres | Yards | 1.094 | 100 m = 109.4 yd |
| Miles | Kilometres | 1.609344 (exact) | 10 miles = 16.09 km |
| Kilometres | Miles | 0.6214 | 10 km = 6.21 miles |
Unlike pints and gallons, these length units are identical in the UK and the US. An inch in a British DIY shop is the same 25.4 mm as an inch in an American catalogue.
How do you convert centimetres to inches?
Divide the number of centimetres by 2.54. A 30 cm ruler is 30 ÷ 2.54 = 11.81 inches long, just short of a foot. Going the other way, multiply inches by 2.54: a 32-inch waist is 81.28 cm. For millimetres, divide by 25.4 instead, so a 15 mm pipe is 0.59 inches across.
The dedicated cm to inches converter and inches to cm converter include printable charts and tape-measure fractions if you are working from an imperial tape.
How do you convert feet and inches to centimetres?
Turn the height into inches first, then multiply by 2.54. Multiply the feet by 12, add the remaining inches, and convert the total. For someone who is 5 ft 9 in, that is 5 × 12 + 9 = 69 inches, and 69 × 2.54 = 175.26 cm, usually rounded to 175 cm.
To reverse it, divide centimetres by 2.54 to get total inches, then divide by 12. The whole number is the feet and the remainder is the inches. The chart below covers common adult heights.
| Feet and inches | Total inches | Centimetres |
|---|---|---|
| 5 ft 0 in | 60 in | 152.4 cm |
| 5 ft 3 in | 63 in | 160.0 cm |
| 5 ft 6 in | 66 in | 167.6 cm |
| 5 ft 9 in | 69 in | 175.3 cm |
| 6 ft 0 in | 72 in | 182.9 cm |
| 6 ft 3 in | 75 in | 190.5 cm |
For other heights, use the feet to cm converter or the cm to feet converter.
How do you convert miles to kilometres?
Multiply miles by 1.609344, or by 1.6 for a quick mental estimate. A 26.2-mile marathon is 26.2 × 1.609344 = 42.16 km; the official distance is 42.195 km, which is 26.22 miles. To turn kilometres into miles, multiply by 0.6214, or use the old rule of thumb that 8 km is roughly 5 miles.
| Distance | Kilometres | Miles |
|---|---|---|
| Parkrun | 5 km | 3.11 miles |
| 10K race | 10 km | 6.21 miles |
| Half marathon | 21.0975 km | 13.11 miles |
| Marathon | 42.195 km | 26.22 miles |
| One mile | 1.609 km | 1 mile (1,760 yd) |
| Running track lap | 400 m | 437.4 yd |
The miles to km converter and km to miles converter give exact answers for any distance.
Why do UK road signs use yards as well as miles?
Short distances on British road signs are given in yards because the road network never switched from imperial units. You will see “200 yds” on signs for junctions and lay-bys, and the three, two and one bar countdown markers before a motorway exit are placed at 300, 200 and 100 yards. A yard is 0.9144 m, so 100 yards is just over 91 metres.
Height and width limits for bridges and narrow roads are often shown in both feet and inches and metres. Drivers of tall vehicles should know their vehicle height in both units, because a 4.0 m van is 13 ft 1.5 in tall, and rounding the wrong way can be costly.
What are chains, furlongs, hands and fathoms?
They are older British length units that survive in sport, horse racing and navigation. Each has an exact metric equivalent because it is defined from the yard or the foot.
| Unit | Imperial definition | Metric equivalent | Where you still meet it |
|---|---|---|---|
| Hand | 4 inches | 10.16 cm | Horse and pony heights |
| Fathom | 6 feet | 1.8288 m | Water depth on older charts |
| Rod, pole or perch | 5.5 yards | 5.0292 m | Older land and allotment descriptions |
| Chain | 22 yards | 20.1168 m | Length of a cricket pitch |
| Furlong | 220 yards | 201.168 m | Horse racing distances |
| Nautical mile | 1,852 m (defined in metric) | 1.852 km | Sea and air navigation |
What mistakes should you avoid when converting lengths?
Most length errors come from rounding too early or misreading decimal feet. Watch for these:
- Using 2.5 instead of 2.54. The shortcut is 1.6 per cent out. On a height of 6 ft (72 in) it gives 180 cm instead of 182.88 cm, almost 3 cm short.
- Treating 5.9 ft as 5 ft 9 in. Decimal feet are not feet and inches. 5.9 ft is 5 ft 10.8 in, because 0.9 × 12 = 10.8.
- Mixing millimetres and centimetres. UK building plans and kitchen units are drawn in millimetres, so a 600 on a drawing means 600 mm (60 cm), not 600 cm.
- Converting a rounded figure. Convert the original measurement once and round at the end, rather than converting a value that has already been rounded.
Accurate conversion starts with an accurate reading. If your tape has both scales, the guide on how to read a tape measure explains the markings in millimetres and in fractions of an inch.
Length converters and guides in this section
New length and distance guides are added to the list below as they are published. These converter pages and related guides are available now:
- Length converter: every common metric and imperial length unit in one tool.
- CM to inches and inches to cm: small measurements, sizes and screen diagonals.
- CM to feet and feet to cm: heights and room dimensions.
- Km to miles and miles to km: running, cycling and driving distances.
- How to measure a TV screen size: why a 55-inch screen is 139.7 cm corner to corner.
Latest length and distance guides
Related sections
The units of measurement guide explains how the metre is defined and how SI, metric and imperial units relate. For measuring rooms and land, see area and property measurement, and for choosing and using rulers, tapes and laser measures, see measuring tools and techniques.
Frequently asked questions
How many centimetres are in an inch?
There are exactly 2.54 centimetres in an inch. The value has been fixed by international agreement since 1959, so 10 inches is 25.4 cm and 12 inches is 30.48 cm.
How many feet are in a metre?
One metre is 3.28 feet, or 3 feet 3.37 inches. To convert metres to feet, multiply by 3.281; to convert feet to metres, multiply by 0.3048.
How many kilometres are in a mile?
One mile is exactly 1.609344 kilometres, which is 1,760 yards. A quick estimate is to multiply miles by 1.6, so 50 miles is roughly 80 km.
Are UK and US inches the same?
Yes. The UK and the US both use the international inch of 25.4 mm, so inches, feet, yards and miles are identical in both countries. Volume units such as pints and gallons do differ.
How tall is 5 ft 10 in in centimetres?
5 ft 10 in is 70 inches, and 70 × 2.54 = 177.8 cm, which is usually rounded to 178 cm.
Sources
- The International System of Units (SI Brochure), BIPM: definition of the metre
- National Physical Laboratory, the UK’s national measurement institute
- Weights and Measures Act 1985, Schedule 1 definitions of units, legislation.gov.uk
- Know your traffic signs, Department for Transport
- Ordnance Survey, national mapping agency for Great Britain