The legal minimum
In the UK, the legal minimum tyre tread depth is 1.6mm, measured across the central three-quarters of the tyre's width, and around its entire circumference. That last part matters — a tyre can look fine at one point and still be illegal if it's worn unevenly and dips below 1.6mm anywhere in that central band.
This limit applies to cars, and to light trailers. Motorcycles and larger vehicles have their own specific requirements, but for most drivers, 1.6mm is the number to know.
How to check your tread depth
You don't need special equipment to get a reasonable read on your tyres. The most common method:
The 20p test
Take a 20 pence coin and insert it into the main tread grooves at several points around the tyre. If the outer rim of the coin — the border around the milled edge — disappears into the groove, your tread is likely above the legal limit at that point. If you can still see the outer rim clearly, it's worth getting the tyre checked properly, since you may be close to or below the legal minimum.
Repeat this at three or four points around the tyre, not just one spot, since wear isn't always even.
Tread wear indicator bars
Most modern tyres also have built-in wear indicator bars — small raised sections within the tread grooves themselves. When the tread has worn down level with these bars, the tyre has reached the legal minimum and needs replacing.
Not sure what you're looking at? This is exactly what we check on every mobile tyre fitting callout — we'll give you a straight answer on whether a tyre is legal, and whether it's a repair or replacement situation. See our Mobile Tyre Fitting service →
What happens if you're caught driving on illegal tyres
Driving on a tyre below the legal tread depth is a specific, separately punishable offence in the UK. The penalty is up to £2,500 and 3 penalty points per tyre. That "per tyre" detail is the part people underestimate — if all four tyres on a vehicle are illegal, that's a theoretical maximum of 12 penalty points and £10,000 in fines, which is well beyond the points threshold that can lead to a driving ban for newer drivers in particular.
Beyond the legal risk, worn tyres measurably increase stopping distances, especially in wet weather, and significantly increase the risk of a blowout — which is a far more dangerous and expensive situation to deal with than simply replacing a tyre before it becomes a problem.
Why tread depth matters beyond the legal minimum
1.6mm is the legal floor, not necessarily the safe practical limit. Many tyre manufacturers and safety organisations recommend considering replacement at 3mm, particularly for tyres used regularly in wet conditions, since braking performance drops off noticeably as tread wears down — well before you hit the legal minimum.
Think your tyres might be close to the limit?
The short version
- Legal minimum: 1.6mm, across the central three-quarters of the tyre, all the way round.
- Check it yourself with the 20p test, or look for the built-in wear indicator bars.
- Penalty for illegal tread: up to £2,500 and 3 points, per tyre.
- Consider replacing earlier than the legal minimum, especially for wet-weather performance.