Tyre tread depth: the UK legal limit and how to check it
8 min readBy Wheel Fit
The short answer: the UK legal minimum tread depth for a car tyre is 1.6mm, measured across the central three-quarters of the tread and around the whole circumference. Below that the tyre is illegal, and the penalty is up to £2,500 and 3 penalty points per tyre.
How to check your tread depth in about a minute
You do not need a gauge, though a gauge is more accurate and costs very little. The quickest check uses a 20p coin:
- Push the coin into a main tread groove.
- If the outer band of the coin is hidden by the tread, you have more than roughly 3mm left — comfortably legal.
- If you can see the outer band, the tread is getting low. Have it measured properly with a gauge.
Do this in at least three places across the tyre — inner edge, middle and outer edge — and on all four tyres. Tyres rarely wear evenly, and the legal limit applies to the worst point in the measured band, not the average.
Do not rely on the tread wear indicators alone
Every tyre has small raised bars set into the main grooves. When the tread is flush with those bars, the tyre is at 1.6mm — which means it is already at the legal limit, not approaching it. They are a last warning, not a planning tool.
Where the 1.6mm actually applies
This is the part most people get wrong. The requirement is not "1.6mm somewhere on the tyre". It is 1.6mm across a continuous band making up the central three-quarters of the tread width, around the entire circumference.
That has two practical consequences. A tyre worn bald on the inner shoulder can still be illegal even if the middle looks fine, once the wear reaches into that central band. And a tyre that is legal at one point on the circumference can be illegal a quarter-turn further round, which is why you should roll the car forward and check again.
Why 1.6mm is the legal floor, not a target
Tread exists to clear water. As the grooves shallow, the volume of water they can move per second falls, and the speed at which the tyre starts to aquaplane drops with it. The loss is gradual and largely invisible in dry weather, which is exactly why worn tyres catch people out in the first heavy rain.
Common industry advice is to replace at around 3mm rather than run to the limit. That is a recommendation rather than a legal requirement — but if you do a lot of motorway miles in winter, it is the more sensible number to work to.
Different limits apply to different vehicles
| Vehicle | Minimum tread | Measured across |
|---|---|---|
| Cars, light vans, light trailers | 1.6mm | Central three-quarters, whole circumference |
| Motorcycles over 50cc | 1mm | Three-quarters, continuous band |
| Large vehicles and passenger-carrying vehicles | 1mm | Three-quarters, continuous band |
If you tow, note that light trailers and caravans fall under the same 1.6mm requirement as cars — though on those, age is usually the limiting factor rather than wear. See caravan and trailer tyres.
What it costs to ignore
| Situation | Consequence |
|---|---|
| Tread below 1.6mm in the measured band | Up to £2,500 fine and 3 penalty points, per tyre |
| All four tyres below the limit | 12 penalty points — enough to lose your licence |
| Tyre condition at MOT | Failure item — see tyre faults that fail an MOT |
The "per tyre" part is what surprises people. Illegal tyres are not one offence with one penalty; each one counts separately.
Other things worth checking at the same time
- Pressure. Under-inflation wears both shoulders and raises fuel consumption. The correct pressures are on a plate in the driver's door shut or inside the fuel flap.
- Uneven wear. Wear concentrated on one edge usually points at alignment or suspension rather than the tyre itself. Replacing the tyre without fixing the cause just wears out the new one.
- Age and cracking. Look for fine cracks in the sidewall rubber. Tyres degrade with time as well as mileage, which matters on low-mileage and seasonal vehicles.
- Bulges. A bulge in the sidewall means the internal structure has failed. That tyre needs replacing now, regardless of how much tread is left.
Common questions
- Is 3mm the legal limit?
- No. 1.6mm is the law; 3mm is a widely-held recommendation based on wet braking performance. Anyone telling you 3mm is a legal requirement is wrong — though we would still advise changing before you reach 1.6mm.
- Does the 20p test actually work?
- As a screening check, yes — the outer band of a 20p sits close to the legal minimum, so if you can see it, measure properly. It is an indicator, not a measurement.
- My tyre is legal in the middle but bald on the inside edge. Is that a problem?
- Very likely yes — once wear reaches into the central three-quarters it is illegal, and inner edge wear usually means an alignment fault that will do the same to the new tyre. See uneven tyre wear.
- How long does 1mm of tread last?
- There is no reliable figure — it depends on the car, the driving and the tyre. That is why checking monthly beats estimating.
- Can a tyre with plenty of tread still need replacing?
- Yes. Age, cracking, bulges and previous damage all end a tyre's life independently of tread. See how to tell if a tyre needs replacing.
If you are close to the limit
You do not have to drive to a garage on tyres you are not confident in. We fit replacement tyres at your home or workplace, so a borderline tyre can be changed on the driveway rather than on a trip you would rather not make.
See the tyre brands and sizes we carry, or read what to do if a tyre fails on the motorway.
