📜 UK Law Explained
Is the Stone a Legal Unit in the UK?
The surprising answer: the stone is legally defined but not permitted for trade. You can weigh yourself in stone, but no shop in Britain can sell you anything weighed in stone. Here is what the law actually says.
The Law Draws a Line: Trade vs Everything Else
British weights and measures law does not ban units outright. It bans them for trade, which means the buying and selling of goods. The Weights and Measures Act 1985, Schedule 11, removed the stone (along with the hundredweight, quarter, dram, and others) from the list of units that may be used when goods are weighed for sale.
This distinction is the whole story. Parliament never made it illegal to think or speak in stone. Bathroom scales, gym conversations, newspaper headlines about celebrity weight loss, and your GP telling you that you are "12 stone" are all completely lawful. What is unlawful is a butcher selling you "a stone of mince" or a market stall pricing potatoes per stone.
The stone's odd position, defined in law but barred from commerce, is a direct result of Britain's half-finished metrication. Our UK metrication history explains how the country ended up with this split system.
What the Weights and Measures Act 1985 Actually Says
The 1985 Act consolidated earlier weights and measures law and brought Britain into line with the European directive on units of measurement (80/181/EEC). Its key provisions for the stone:
- Stone removed for trade: Schedule 11 lists the stone among units that may no longer be used for trade, except on weighing equipment that was already in use before 1 December 1980 (a grandfather clause for old scales).
- Metric units mandatory: goods sold by weight must be sold in grams and kilograms. Imperial equivalents may appear as supplementary indications, but the metric figure must be the prominent one.
- Stone still defined: the Act defines the stone as exactly 14 pounds, which through the legal definition of the pound (0.45359237 kg) makes the stone exactly 6.35029318 kg. The definition survives even though trade use does not.
The earlier Units of Measurement Regulations 1978 and 1980 had already begun phasing imperial units out of trade, and the 1994 Regulations completed the job for most retail. By 2000, loose goods like fruit, vegetables, and meat had to be sold in metric, which is why supermarket scales today show kilograms.
Where Stone Is (and Is Not) Legally Recognised
| Context | Stone allowed? |
|---|---|
| Selling goods by weight (shops, markets) | No, metric only |
| Personal body weight (scales, conversation) | Yes |
| GP consultations and NHS records | Yes (records kept in kg; stone used conversationally) |
| Newspapers and broadcasters (BBC etc.) | Yes |
| Horse racing and boxing weights | Yes (sporting convention) |
| Official statistics and government data | No, metric |
| Supplementary labelling on packaging | Yes, alongside metric |
Notice the pattern: wherever money changes hands for a measured quantity, metric rules. Everywhere else, custom rules. This is why Britain feels metric in the supermarket and imperial on the bathroom scales.
Enforcement: Trading Standards and the "Metric Martyrs"
The law is enforced by Trading Standards officers working for local authorities. They inspect shop scales, check that they are metric and properly stamped, and can prosecute traders who sell in unauthorised units. The most famous enforcement case was that of Sunderland greengrocer Steven Thoburn, convicted in 2001 for using imperial-only scales. He became known as the "metric martyr", and his case made the stone's legal position national news.
In practice, prosecutions are rare today because compliance is near-universal in retail. The battleground has moved to labelling: the EU long permitted imperial units as supplementary indications, and after Brexit the UK government consulted on allowing shops to sell in pounds and ounces again. Whatever the outcome of those reviews, the stone's position is unchanged: defined in law, barred from trade, free for everything else.
Practical note: because the stone is legally defined as exactly 6.35029318 kg, conversions to and from stone are exact, not approximate. Use our stone to kg chart or read what a stone is for the definition in full.
Frequently Asked Questions
Is the stone a legal unit of measurement in the UK?
The stone is legally defined as exactly 6.35029318 kg, but it is not permitted for trade. The Weights and Measures Act 1985 removed the stone from the list of units allowed for selling goods, so shops cannot price or sell in stone.
Can shops in the UK sell goods weighed in stone?
No. Since the Weights and Measures Act 1985 (in line with EU directive 80/181/EEC), goods sold loose must be weighed in metric units. Supplementary imperial indications are allowed on packaging, but the metric figure must be the prominent one.
Is it illegal to use stone for body weight in the UK?
Not at all. The law only governs trade, meaning buying and selling. Using stone for your own body weight, in conversation, in the media, or at the gym is completely legal and always has been.
Who enforces weights and measures law in the UK?
Trading Standards officers, employed by local authorities, enforce the Weights and Measures Act 1985. They check that shops use approved metric weighing equipment and that quantities stated on goods are accurate.
Did Brexit change the legal status of the stone?
No. The Weights and Measures Act 1985 remains in force, and the stone is still not permitted for trade. Post-Brexit reviews discussed allowing more imperial labelling, but the stone's legal position has not changed.