The UK legal tyre tread depth is 1.6mm. It must be met across the central three-quarters of the tyre's width and around its entire circumference, and it applies to cars, vans and light vehicles. A tyre that falls below it is illegal, fails the MOT, and is far less safe in the wet.
How the limit is measured
The rule is more specific than a single number. The 1.6mm must be present:
- across the central three-quarters of the tread width, and
- around the whole circumference of the tyre
The practical effect is that one worn strip is enough to fail. If any part of that central band drops below 1.6mm anywhere around the tyre, the whole tyre is illegal, even if the rest still has plenty of tread. Wear is often uneven, so a tyre that looks fine across most of its face can still be illegal on one edge.
The limit applies to the primary grooves, the main ones, which carry the tread wear indicators. Some tyres have shallower secondary grooves by design, and those are not where the measurement is taken.
Why 1.6mm is legal but not safe
New tyres start with roughly 8mm of tread, around five times the legal minimum. By the time a tyre reaches 1.6mm it has lost most of its ability to clear water, and that is where the danger lies.
Independent testing has long shown that wet braking deteriorates sharply once tread drops below 3mm. The difference in wet stopping distance between a tyre worn to 3mm and one worn to 1.6mm can be as much as 44%, and from motorway speeds that is a difference measured in car lengths. For that reason, safety organisations and tyre manufacturers advise replacing at around 3mm rather than running tyres down to the legal floor; a fresh set well before the limit is the safer habit, easy to order online from the likes of Tyres.co.uk. Legal and safe are not the same thing.
Checking the depth
There are three reliable ways to check, covered fully in their own guides:
- The tread wear indicators moulded into the grooves sit at exactly 1.6mm, so when the surrounding tread is level with them the tyre is at the limit
- A tread depth gauge gives an exact figure in millimetres
- The 20p test is a quick rough check: if the coin's outer band is hidden in the groove, the tread is likely above the limit
Because tyres wear unevenly, any check should be taken at several points across the width and around the tyre, not just one spot.
A note on other vehicles
The 1.6mm figure is the one almost every driver needs, covering cars, vans and light vehicles. Some other vehicle types have different requirements, motorcycles over a certain engine size, for example, have their own lower limit, so riders and operators of specialist vehicles should check the rule that applies to them.
From the workshop: the part that catches people out is that it only takes one worn strip to make a tyre illegal. We regularly see tyres with healthy tread across most of the face but a bald inner edge, and that tyre is just as illegal as a bald one, as well as being a clear sign something needs looking at.
Sources and accuracy. The 1.6mm limit, the central three-quarters and full-circumference wording, and the wet-braking figures here reflect UK law and published safety research at the time of writing. Tyre law can change, so anything safety-critical should be confirmed against current official guidance. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What is the legal tread depth for tyres in the UK?+
1.6mm, across the central three-quarters of the tyre's width and around its entire circumference. This applies to cars, vans and light vehicles. New tyres usually start with around 8mm of tread.
Is one worn patch enough to make a tyre illegal?+
Yes. If any part of the central three-quarters of the tread falls below 1.6mm at any point around the circumference, the whole tyre is illegal, even if the rest of the tread is fine.
Should I really wait until 1.6mm to replace my tyres?+
No. The 1.6mm limit is a legal floor, not a safe target. Safety bodies and tyre makers recommend replacing at around 3mm, because wet braking and grip fall away sharply below that point, well before the legal limit is reached.
How do I know when a tyre reaches 1.6mm?+
The tread wear indicators built into the grooves sit at 1.6mm, so when the tread wears level with them the tyre is at the limit. A tread depth gauge gives an exact figure, and the 20p test is a quick rough check.