Tyre Tread Depth: The UK Legal Limit and Why It Matters

Published 2026-05-23 · Park Royal Tyre & Alignment Centre

Your tyres are the only part of your car that actually touches the road. That contact patch, on each tyre, is roughly the size of the palm of your hand. Everything you ask your car to do, accelerating, braking, steering, cornering in the rain, depends on those four small areas of rubber gripping the tarmac. When the tread wears down, that grip fades, and the risk climbs quietly until the day you really need it. Knowing the legal limit, and knowing when to act before you reach it, is one of the simplest ways to keep yourself and other road users safe.

What is the UK legal tread depth limit?

The legal minimum tread depth for cars in the UK is 1.6mm. That figure isn't measured at a single spot, though. The law requires at least 1.6mm across the central three-quarters of the tyre's width, and around its entire circumference. In other words, the middle band of the tyre, all the way round, must meet the limit.

Why does the measurement method matter? Because tyres rarely wear evenly. A tyre can look fine on the outer edges while the centre has worn smooth, or it might be perfectly legal in one spot and bald a quarter-turn later. That's why a proper check looks at several points around and across each tyre, not just the first place you happen to glance.

How do you do the 20p test?

The 20p test is the easiest way to get a rough reading without any tools. Take a 20 pence coin and slot it into the main grooves of your tyre. If the raised outer band around the edge of the coin disappears into the tread, your depth is probably comfortably above the legal limit. If you can still see that band, your tyres may be close to, or below, 1.6mm and need a closer look.

Repeat the check at several points across the width of each tyre and at a few places around the circumference. The 20p test is a handy first warning, not a precise measurement. If the result looks borderline, treat it as a prompt to get the tyres measured properly with a tread depth gauge.

Why does tread depth matter so much in the wet?

Tread does one crucial job in the rain: it clears water out of the way so the rubber can still touch the road. The grooves channel water away from the contact patch. As the tread wears down, those grooves get shallower and shift less water, so braking distances stretch and the risk of aquaplaning rises sharply on standing water.

This is the part many drivers underestimate. In the dry, a worn tyre might feel perfectly normal right up to the legal limit. It's in heavy rain, on a fast slip road or an emergency stop, that the difference between healthy tread and worn tread suddenly becomes obvious. By then it's too late to do anything but hope. Healthy tread is your insurance against the weather you can't control.

What are the penalties for illegal tyres?

Driving on illegal tyres is taken seriously. A tyre below the 1.6mm legal limit is illegal to use on the road. On top of that, if you're stopped on the road with tyres under the limit, you can face a fine and penalty points for each illegal tyre. With four worn tyres, those points and fines stack up fast, and the consequences for your licence can be severe.

Tread wears down gradually, though. A tyre that was legal a few months ago can drop below the limit long before you'd otherwise notice, especially if you cover a lot of miles. That's why your own regular checks matter so much. Don't rely on an occasional inspection alone to catch a worn tyre.

Why replace tyres early at around 3mm?

Many tyre experts recommend replacing tyres at around 3mm rather than waiting for 1.6mm. The reasoning is straightforward: wet grip and braking performance start to fall away noticeably as tread gets thin, well before you reach the legal floor. Acting at 3mm gives you a useful safety margin instead of running your tyres right to the edge.

There's a practical angle too. Tyres don't wear at a steady pace, and the last couple of millimetres can disappear quickly. Replacing a little early means you're never caught out by a tyre that slips below the limit between checks. It also spreads the cost over time, since you're rarely forced to replace several tyres at once in a panic. Think of 3mm as a sensible planning point, not a hard rule.

How do you get your tread depth checked?

The reliable way to know exactly where your tyres stand is a professional measurement with a calibrated gauge, taken across the width and around each tyre. A quick visual check at home is great for spotting obvious problems, but a proper inspection catches uneven wear, edge damage and slow punctures that a glance can miss. It only takes a few minutes.

At Park Royal Tyre & Alignment Centre we check tread depth as part of our routine tyre work, and we can advise honestly on whether you need new rubber now or can safely wait. If a tyre is worn, our tyre fitting and repair service covers everything from a single replacement to a full set, and you can browse options on our tyres page.

Frequently asked questions

What is the minimum legal tread depth in the UK?

For cars, the minimum legal tread depth is 1.6mm. It must be maintained across the central three-quarters of the tyre's width and around the tyre's entire circumference. Anything below that limit is illegal to use on the road.

Is the 20p test accurate?

The 20p test is a reliable quick check, not an exact measurement. If the coin's outer band is hidden inside the tread groove, your depth is likely above 1.6mm. If the band shows, get the tyre measured with a proper tread depth gauge to be sure.

Should I really replace tyres at 3mm?

Replacing at around 3mm is widely recommended because wet braking and grip decline well before the 1.6mm legal limit. It gives you a safety margin and means you're less likely to be caught driving on a tyre that has dropped below the limit between checks.

How often should I check my tyres?

A monthly visual check is a sensible habit, plus a look before any long journey. Watch for uneven wear, cuts, bulges and low tread. If anything looks borderline, book a professional inspection rather than putting it off.

Not sure where your tread stands? Don't leave it to guesswork. Pop into Park Royal Tyre & Alignment Centre in Park Royal, London NW10 7TR for a quick, honest tread check from an RAC and AA approved team. Call us on 020 3886 2355, message us on WhatsApp at 07476 586 589, or get in touch here to book a convenient time.