UK Unit Conversion: Metric and Imperial Guide
The United Kingdom has a unique measurement situation that confuses visitors and sometimes even residents. Unlike most countries, which use metric only, and unlike the United States, which uses imperial almost exclusively, the UK uses both systems simultaneously depending on the context.
Understanding which system applies where makes everyday life much easier. This guide covers the most common unit situations in the UK and links you to the free conversion tools on CalConvs. Browse all converters at the Unit Converters hub.
Road Distances and Speed: Imperial
Every road sign in the UK shows distances in miles and speed limits in miles per hour (mph). This is one of the most visible examples of imperial measurement in daily UK life.
UK Road Speed Reference
20 mph = 32.2 km/h (residential zones and school areas)
30 mph = 48.3 km/h (built-up areas, the most common urban limit)
40 mph = 64.4 km/h (some urban and semi-rural roads)
50 mph = 80.5 km/h (single carriageway rural roads in some areas)
60 mph = 96.6 km/h (national speed limit on single carriageways)
70 mph = 112.7 km/h (motorways and dual carriageways)
If you are visiting from Europe, Australia or anywhere metric, use the Speed Converter and Length Converter to make sense of UK road signs.
Body Weight: Stone, Pounds and Kilograms
Most British people describe their body weight in stone and pounds, which is rare outside the UK and Ireland. Doctors and hospitals use kilograms. Gym equipment and fitness apps use kilograms. Everyday conversation uses stone and pounds.
| Stone | Kilograms | Pounds |
|---|---|---|
| 8 stone | 50.8 kg | 112 lbs |
| 9 stone | 57.2 kg | 126 lbs |
| 10 stone | 63.5 kg | 140 lbs |
| 11 stone | 69.9 kg | 154 lbs |
| 12 stone | 76.2 kg | 168 lbs |
| 13 stone | 82.6 kg | 182 lbs |
| 14 stone | 88.9 kg | 196 lbs |
| 15 stone | 95.3 kg | 210 lbs |
| 16 stone | 101.6 kg | 224 lbs |
Use the Weight and Mass Converter to convert between stone, pounds and kilograms instantly. When entering your weight into health tools like the BMI Calculator or BMR Calculator, convert to kilograms first.
Height: Feet and Inches vs Metres
Like weight, height in the UK is commonly described in feet and inches in everyday conversation, while medicine and official records use metres and centimetres.
| Feet and Inches | Centimetres | Metres |
|---|---|---|
| 5 ft 0 in | 152.4 cm | 1.524 m |
| 5 ft 2 in | 157.5 cm | 1.575 m |
| 5 ft 4 in | 162.6 cm | 1.626 m |
| 5 ft 6 in | 167.6 cm | 1.676 m |
| 5 ft 8 in | 172.7 cm | 1.727 m |
| 5 ft 10 in | 177.8 cm | 1.778 m |
| 6 ft 0 in | 182.9 cm | 1.829 m |
| 6 ft 2 in | 187.9 cm | 1.879 m |
Temperature: Celsius Official, Fahrenheit Informal
The UK officially uses Celsius for weather forecasts, cooking and science. Older British people sometimes still think in Fahrenheit, and some tabloid newspapers report temperatures in both. Medical body temperature is always in Celsius.
| Celsius | Fahrenheit | Context |
|---|---|---|
| -5 C | 23 F | Frosty, roads may ice |
| 0 C | 32 F | Freezing point, snow possible |
| 10 C | 50 F | Cold British day |
| 15 C | 59 F | Cool spring day |
| 20 C | 68 F | Pleasant summer day |
| 25 C | 77 F | Warm, considered hot by many UK residents |
| 30 C | 86 F | Very hot for the UK, heatwave conditions |
| 37 C | 98.6 F | Normal body temperature |
Use the Temperature Converter to switch between Celsius and Fahrenheit for any context.
Drinks: Pints for Beer, Litres for Soft Drinks
Draught beer and cider in UK pubs is served in pints. The UK pint (568ml) is larger than the US pint (473ml). Bottled and canned drinks are sold in metric sizes. Petrol and diesel are sold in litres.
UK Pint Conversions
1 UK pint = 568 ml = 0.568 litres
1 UK pint = 1.2 US pints (the UK pint is larger)
1 UK pint = 20 UK fluid ounces
1 litre = 1.76 UK pints
If a US recipe calls for a pint, it means 473 ml, not 568 ml.
Use the Volume Converter for all liquid volume conversions including pints, litres, cups and fluid ounces.
Food Quantities: Metric in Shops, Imperial in Old Recipes
UK supermarkets sell food in metric quantities. However, traditional British recipes from books printed before the 1970s often use pounds and ounces. Many home bakers still think in ounces.
| Imperial | Metric |
|---|---|
| 1 oz | 28.35 g |
| 2 oz | 56.7 g |
| 4 oz (quarter pound) | 113.4 g |
| 8 oz (half pound) | 226.8 g |
| 1 lb (16 oz) | 453.6 g |
| 500 g (half kg) | 17.6 oz |
| 1 kg | 35.3 oz or 2 lb 3.3 oz |
UK Health Metrics: Using CalConvs
The UK National Health Service uses metric units for all clinical measurements. When using CalConvs health tools, enter values in the units specified.
- BMI Calculator: enter height in metres and weight in kilograms (use the weight converter if you know your weight in stone)
- Calorie Calculator: works in metric units, results apply regardless of location
- Ideal Weight Calculator: results shown in both kg and lbs for UK convenience
Related Tools for UK Users
- Weight and Mass Converter: stone, pounds and kilograms
- Length Converter: feet, inches, miles and metric equivalents
- Temperature Converter: Celsius and Fahrenheit
- Volume Converter: UK pints, litres, cups and fluid ounces
- Speed Converter: mph and km/h
- All Unit Converters: browse all converters on CalConvs
Frequently Asked Questions
Why does the UK still use miles for roads?
The UK converted to metric for most purposes in the 1970s and 1980s, but road signs were exempted from metrication due to the enormous cost and disruption of changing every sign simultaneously. There have been periodic discussions about converting road signs to kilometres, but no firm government commitment has been made. Until then, UK roads remain imperial.
How many kilograms is a stone?
One stone is exactly 14 pounds, which equals approximately 6.35 kilograms. To convert stone to kilograms, multiply the number of stone by 6.35. For example, 11 stone equals 11 × 6.35 = 69.85 kg. For a more precise conversion or to include extra pounds, use the Weight and Mass Converter.
Is the UK pint the same as the US pint?
No. The UK pint is 568 ml while the US pint is 473 ml. The UK pint is approximately 20 percent larger. This difference matters when following American recipes or comparing drink sizes. The UK uses this larger pint measurement for both the imperial fluid pint and for pub serving sizes.
What units does the NHS use?
The NHS uses metric units for all clinical measurements: kilograms for weight, metres and centimetres for height, Celsius for temperature, millimetres of mercury (mmHg) for blood pressure and millimoles per litre (mmol/L) for blood glucose and cholesterol. If you have health measurements in imperial units, convert them to metric before entering them into NHS digital health tools.