How to Check Tyre Tread Depth: A Complete Safety Guide
Learn how to check tyre tread depth with a gauge, a coin, and the built-in wear bars, plus when to replace worn tyres before they fail.
Knowing how to check tyre tread depth is one of the simplest, cheapest safety habits you can build, and it takes under five minutes per wheel. Tread is what channels water away from the contact patch and grips the road when you brake or corner, so as it wears down your stopping distances grow and the risk of aquaplaning climbs sharply. This guide walks you through three reliable ways to measure tread depth, how to read the results, and exactly when a tyre needs replacing.
Why tread depth matters
A new car tyre typically starts life with around 8 mm of tread. As those grooves wear shallower, the tyre loses its ability to disperse water and maintain grip. The difference is not subtle: on a wet road, a tyre at 3 mm can stop noticeably sooner than one at the legal minimum, and the gap widens the faster you are travelling.
Most regions set a minimum legal tread depth of 1.6 mm across the central three-quarters of the tyre, around its entire circumference. That figure is a legal floor, not a safety target. Many tyre engineers and safety bodies recommend replacing tyres well before that point, particularly if you regularly drive in heavy rain.
| Tread depth | Condition | What it means |
| 8 mm | Brand new | Full grip and water clearance |
| 4-5 mm | Good | Still performs well in the wet |
| 3 mm | Consider replacing | Wet grip starting to fall off |
| 1.6 mm | Legal minimum | Replace now; grip is compromised |
| Below 1.6 mm | Illegal & unsafe | Immediate replacement required |
Method 1: Use a tread depth gauge
A dedicated tread depth gauge is the most accurate tool and costs only about $5 to $15. It gives you a precise reading in millimetres, which matters when you are trying to decide whether a tyre has a season left in it.
- Park on level ground with the handbrake on and the engine off.
- Push the probe pin of the gauge fully down into one of the main grooves until the base sits flat on the tread blocks.
- Read the measurement where the scale meets the body of the gauge.
- Repeat in at least three points across the width of the tyre (inner, centre, outer) and at three points around the circumference.
- Record the lowest reading, because a tyre is only as safe as its most worn section.
Measuring in several spots is essential. A tyre can look fine in the centre yet be worn to the cords on an inner edge, which is a classic sign of an alignment or pressure problem.
Method 2: The coin test
No gauge to hand? A coin gives a quick pass/fail check. Use any coin with a clear outer band or raised rim, insert it into the main groove, and see how much of the rim disappears.
- If the outer band of the coin is completely hidden by the tread, you likely have a safe amount of tread remaining.
- If the band is visible, your tread is getting low and you should measure it properly with a gauge.
The coin test is a screening tool, not a precise measurement. Treat a borderline result as a prompt to check with a proper gauge rather than a green light.
Method 3: Read the tread wear indicators
Every modern tyre has built-in tread wear indicators (TWIs), sometimes called wear bars. These are small raised bridges of rubber moulded into the bottom of the main grooves, set at exactly 1.6 mm.
To find them, look for a small triangle symbol, the letters "TWI", or a tiny logo moulded into the tyre's sidewall shoulder. Follow that marker inward and you will see the wear bar sitting in the adjacent groove. When the surrounding tread wears down until it is flush with those bars, the tyre has reached the legal limit and must be replaced. If the bars are already level with the tread across the tyre, do not drive on it any longer than necessary.
Reading uneven wear patterns
How a tyre wears tells you as much as the depth itself. Checking across the full width, not just the centre, reveals mechanical faults early.
| Wear pattern | Likely cause | Action |
| Both edges worn, centre fine | Chronic under-inflation | Correct pressures; check for slow leaks |
| Centre worn, edges fine | Over-inflation | Reduce to the placard pressure |
| One inner or outer edge worn | Misalignment (camber/toe) | Get a wheel alignment |
| Patchy or scalloped (cupping) | Worn shocks, bushes or imbalance | Inspect suspension and balance wheels |
| Flat spots | Harsh braking or a locked wheel | Inspect braking; may need replacement |
Uneven wear often points to a fault that will chew through your next set of tyres too, so fix the root cause. A four-wheel alignment usually costs $80 to $150, and it pays for itself in tyre life. If you notice vibration or a warning light alongside the wear, scan for fault codes using an OBD-II code lookup to rule out an ABS or sensor issue before spending on parts.
How often should you check?
Make tread depth part of a simple routine rather than an afterthought:
- Monthly: a quick visual and coin check of all four tyres, including the spare.
- Before long trips: measure with a gauge, especially if the car will be loaded.
- At every service: ask your workshop for the actual millimetre readings.
- After hitting a kerb or pothole: check for damage and uneven wear.
Don't forget the spare. A space-saver or full-size spare that has quietly aged in the boot is no help if it has perished or lost pressure. You can log your readings and set reminders with our free car maintenance tools.
When to replace and what it costs
Replace a tyre when any of these are true: the tread reaches 1.6 mm anywhere across the measured area, the wear bars are flush with the tread, you can see cords or the internal structure, or the sidewall shows cracking, bulges, or cuts. Age matters too. Rubber hardens over time, so many manufacturers advise replacing tyres around six years old and never using one beyond ten years, regardless of tread.
Budget passenger-car tyres typically cost $60 to $120 each fitted and balanced, while performance or larger SUV sizes run $150 to $300 or more. Always replace tyres in pairs on the same axle to keep grip balanced, and fit the newer pair to the rear on most cars to reduce the risk of oversteer in the wet.
Replacing worn tyres and correcting alignment are safety-critical jobs, so if you are unsure about wear patterns or suspension faults, have a qualified mechanic inspect the car before you drive on. For a broader walkthrough of pre-drive checks, see our guide on how to check tyre pressure.
Frequently asked questions
What is the minimum legal tyre tread depth?
In most regions the legal minimum is 1.6 mm across the central three-quarters of the tyre and around its full circumference. However, wet-weather grip drops off well before that, so many experts recommend replacing tyres at around 3 mm rather than waiting for the legal limit.
Can I check tread depth without any tools?
Yes. The coin test gives a rough pass/fail: insert a coin with a raised rim into a main groove and see whether the outer band is hidden. You can also read the built-in wear bars in the grooves. Both are screening checks, so confirm a borderline result with an inexpensive tread depth gauge.
Why is my tyre worn on only one edge?
Wear concentrated on a single inner or outer edge almost always points to wheel misalignment, such as incorrect camber or toe. Left unchecked it will ruin the tyre quickly and affect handling, so book a wheel alignment and have the suspension components inspected for wear.