Imperial (UK) vs Metric
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
UK road distances, human height and weight, pub quantities, rugby and football pitches (yards), older UK maps.
Scientific work, medicine, nutrition labels (since EU alignment), new building plans, all international commerce, cooking weight.
| Aspect | Imperial (UK) | Metric |
|---|---|---|
| Road signs | Miles (required by law) | — |
| Speed limits | mph | — |
| Height (personal) | Feet & inches common | cm increasingly used by under-40s |
| Body weight | Stone and pounds | kg used clinically |
| Pubs | Pints and half-pints | — |
| Supermarket food | grams and ml (legally) | — |
Frequently asked
Is it illegal to use imperial in the UK?
Imperial units are not illegal — they just can't be used as the sole unit in trade (weights and measures for selling). A market stall can show '£2.50/lb' but must also show £/kg. Road signs and beer are explicit legal exceptions where imperial must be used.
Why did Ireland fully switch to metric but the UK didn't?
Ireland converted road signs to km in 2005 as part of a coordinated national programme. The UK government estimated the cost at £750 million+ to replace all road signs, and has declined to do it. Political will has not been there since metrication started in 1965.