Your tyres are the only part of your car that actually touches the road, so their condition has a direct impact on your safety behind the wheel. Knowing how to check tyre tread depth is one of the simplest maintenance tasks you can do yourself, and it takes less than a minute. Yet many Australian drivers put it off until a mechanic flags it during a service, or worse, until worn tyres contribute to an accident.
In every state and territory, driving on tyres below the minimum legal tread depth of 1.5mm is an offence that can result in fines, demerit points, and a defect notice. Beyond the legal side, bald or near-bald tyres significantly increase your stopping distance in wet conditions and raise your risk of aquaplaning. At National Cover, we see firsthand how proper vehicle maintenance supports safer driving, and that starts with roadworthy tyres. Keeping your tread in check helps protect you, your passengers, and your insurance standing.
This guide walks you through three reliable ways to measure your tyre tread: the classic coin test, the built-in tread wear indicators (TWI) moulded into your tyres, and manual tread depth gauges. We’ll also cover when it’s time to replace your tyres and what to look out for between checks. No special tools or mechanical experience required, just a couple of minutes and, optionally, a 20-cent coin.
Know the legal limit and what tread depth means
Before you learn how to check tyre tread depth, it helps to understand what you’re actually measuring and why the number matters. Tread depth is the vertical distance from the top of the tyre’s rubber to the bottom of its deepest groove. Those grooves channel water away from the contact patch between your tyre and the road, maintaining grip in wet conditions. When the grooves wear down, that water has nowhere to go, your stopping distance increases, and your risk of losing control rises significantly.
The 1.5mm legal minimum in Australia
In Australia, the legal minimum tread depth is 1.5mm across the full width of the tyre, including the shoulders. This standard applies in every state and territory under the Australian Road Rules and relevant vehicle standards. If your tread falls below this threshold, your vehicle is considered unroadworthy and you cannot legally drive it. Police and authorised transport inspectors can issue defect notices, on-the-spot fines, and demerit points, and in some states your registration can also be suspended until the tyres are replaced.
A defect notice means your car cannot be driven until you rectify the fault and pass a roadworthy inspection, so catching worn tread early saves you real time and money.
How tread depth affects your safety
New tyres typically start at 6mm to 8mm of tread depth. Grip and water dispersal begin to deteriorate noticeably below 3mm, particularly on wet or greasy roads. By the time you reach 1.5mm, a tyre’s ability to channel water is severely compromised, and your braking distance in wet conditions can be up to twice as long compared to a new tyre. Knowing these numbers gives you a clear benchmark for making smarter, safer decisions about when to replace your tyres.
Step 1. Check the tread wear indicators
Tread wear indicators (TWI) are small rubber bars moulded directly into your tyre’s grooves at a height of exactly 1.5mm, matching the legal minimum in Australia. They give you an instant visual signal without any tools, making them the fastest first check to run before moving on to how to check tyre tread depth by other methods.
How to find the TWI
Look at the sidewall of your tyre for a small triangle symbol or the letters "TWI" moulded into the rubber. These markers point to the location of the wear indicator bars sitting inside the main tread grooves. Most tyres have six or more of these indicators spaced evenly around the circumference, so you get a consistent reading across the full tyre.
If the tread surface is level with any of these bars, your tyre has reached the legal minimum and needs replacing immediately.
Once you spot the markers, crouch down beside each tyre and look along the groove the symbol points to. If the bar sits flush with the surrounding rubber, the tyre is at or below 1.5mm. Do not drive further on a tyre in that condition. Check all four tyres, since wear can differ between the front and rear axles.
Step 2. Do the 20c coin test
The 20-cent coin test is a quick, tool-free way to check tyre tread depth when you don’t have a gauge nearby. Grab any Australian 20-cent coin from your wallet and you’re ready to go in seconds.
How to run the test
Insert the coin into your tyre’s deepest groove with the platypus side facing down and toward you. Hold the coin vertically and push it firmly into the groove. Run this check across multiple points on each tyre, including the centre and both outer shoulders, since tyres often wear unevenly across the width.
If you can see the platypus’s bill clearly above the rubber, your tread is at or below 1.5mm and you need to replace the tyre straight away.
What the result means
A 20-cent coin measures roughly 3mm from its outer edge to the platypus’s bill, giving you a practical reference point. If the surrounding rubber covers the bill completely, your tread depth sits above the legal minimum. If the bill is visible above the tyre surface, treat that tyre as unsafe and replace it before your next drive.
Step 3. Measure with a tread depth gauge
A tread depth gauge gives you the most precise reading of the three methods, and you can pick one up at any auto parts store for under $10. While the coin test tells you whether you’re above or below a rough threshold, a gauge gives you an exact measurement in millimetres, letting you track how quickly your tyres are wearing over time.
How to use a tread depth gauge
Using a gauge is straightforward. Press the probe straight down into the tyre’s deepest groove, making sure the base plate sits flat against the tyre surface. Push the probe down until it stops, then read the number on the dial or digital display. Take readings at three or four points across the tyre width, including the centre and both outer edges, since uneven wear often goes unnoticed without checking multiple spots.
Write down each reading alongside the date, so you can track your wear rate and plan your next replacement before you hit the legal limit.
| Reading | What it means |
|---|---|
| 4mm or above | Good condition |
| 2mm to 3.9mm | Monitor closely |
| 1.5mm to 1.9mm | Replace soon |
| Below 1.5mm | Illegal, replace immediately |
Knowing how to check tyre tread depth with a gauge also helps you spot uneven wear patterns that might point to a wheel alignment or tyre pressure issue worth addressing early.
Step 4. Decide if you need new tyres now
Once you know how to check tyre tread depth and have your measurements in hand, the decision on whether to replace your tyres becomes straightforward. Use the results from Steps 1 to 3 to guide your next action based on the actual depth you recorded.
Use this decision guide
Your readings point clearly to one of three outcomes. Match your result to the table below and act accordingly.
| Tread depth | Action required |
|---|---|
| 3mm or above | Safe to drive, recheck in 3 months |
| 1.5mm to 2.9mm | Book a tyre replacement soon |
| Below 1.5mm | Stop driving, replace immediately |
Watch for uneven wear too
Uneven tread wear across the width of a tyre, such as the outer edges wearing faster than the centre, often signals a wheel alignment or tyre pressure issue. Even if your depth readings sit above 1.5mm, uneven wear can compromise your handling and means you should book a tyre inspection without delay.
If two or more tyres need replacing at the same time, replace them in pairs on the same axle to keep your vehicle balanced and handling predictably.
Quick recap and next steps
You now have three reliable methods for how to check tyre tread depth: the tread wear indicators built into your tyres, the 20-cent coin test you can run without any tools, and a tread depth gauge for an exact millimetre reading. Each check takes under a minute, and together they give you a clear picture of where your tyres stand against Australia’s 1.5mm legal minimum.
Make it a habit to check your tread every three months or before any long road trip. If any tyre sits below 1.5mm, stop driving on it straight away and arrange a replacement before your next trip. When two or more tyres need replacing at the same time, swap them in axle pairs to keep your vehicle balanced and handling predictably.
Tyre maintenance is one part of staying protected on Australian roads. Pairing good vehicle habits with the right motor insurance gives you genuine peace of mind all year. Get a quote from National Cover today and see how much you could save.
