What tread depth is illegal?

2/32 of an inch in the United States and 1.6 mm in the EU and UK — the same depth expressed two ways. The moulded wear bars between the tread blocks sit at exactly that height, so when they are flush with the tread the tire is finished.

Should I replace tires at 4/32 rather than waiting for 2/32?

In wet weather, yes. Below about 4/32" the grooves no longer clear enough water and wet stopping distances grow sharply, which is why many workshops advise replacement there rather than at the legal floor.

How does the penny test compare to a gauge reading?

A penny inserted upside down hides Lincoln's head at roughly 2/32", and a quarter hides Washington's at about 4/32". They are quick checks against those two thresholds, not measurements — a gauge is what gives you a number to track.

How deep is the tread on a new tire?

Around 10/32" for a passenger tire, 11/32" for a touring all-season, 12/32" for light truck and winter tires, and 15/32" or more for all-terrain. The exact figure is usually on the manufacturer's spec sheet.

Does this predict when my tires will actually wear out?

It extrapolates the wear rate you have seen so far, which assumes the driving ahead looks like the driving behind. Rotation, pressure, alignment and how much of your mileage is motorway all shift the real answer.

Tire Tread Depth Calculator

Turn a gauge reading into remaining tread life, a wear rate and the distance left before the legal limit.

The Tire Tread Depth Calculator runs entirely in your browser. Your measurements and mileage are calculated on your device and never sent anywhere.

Compare tire sizes

About Tire Tread Depth Calculator

A tread gauge gives you one number, and that number on its own does not say much. What matters is how far it sits above the legal minimum, how quickly the tread is disappearing, and how much driving is left before the tire has to come off. This calculator takes the depth you measured, the depth the tire had when new and, if you know it, the distance covered so far, and works out all three. Depths convert freely between 32nds of an inch, millimetres and decimal inches, because tread gauges, tire labels and legal limits rarely use the same unit. The coin tests are translated too, so a reading can be checked against a penny or a quarter.

Features

Reads tread depth in 32nds of an inch, millimetres or inches
Remaining usable tread above the legal minimum, and the percentage of life left
Wear rate in 32nds per 1,000 miles or kilometres
Distance the tire should still cover before it reaches the limit
Status against the legal, wet-weather and winter thresholds
Presets for passenger, touring, light truck, all-terrain and winter tread depths
Penny and quarter coin-test equivalents for the depth you entered
Copyable summary of the whole reading

How to use the Tire Tread Depth Calculator

Measure the tread at three points across the tire and take the shallowest reading
Enter that depth and pick the unit your gauge uses
Set the depth the tire had when new, or pick a preset for its type
Add the distance covered on these tires to get a wear rate and the life left

Example

Input

Measured 6/32", new 10/32", 20,000 miles covered

Output

Usable tread 4/32" · 50% of life left · 0.20 per 1,000 mi · about 20,000 miles to go

Half the usable tread is gone at 20,000 miles, so the tire is on course for roughly 40,000.

Common errors & troubleshooting

The calculator says the measurement is deeper than a new tire. — The new depth is probably in a different unit from the measurement. A passenger tire is about 10/32" or 8 mm — check both fields use the same unit before comparing.
The wear rate looks impossibly fast. — Check the distance field is the distance on these tires, not the odometer reading of the car. A set fitted at 30,000 miles on a 50,000-mile car has covered 20,000.
Readings differ across the tire. — That is the useful finding. Wear only on the edges points at underinflation, wear down the middle at overinflation, and wear on one shoulder at alignment.
The remaining distance is blank. — A wear rate needs a distance and some measurable wear. A tire still at its full new depth has nothing to extrapolate from yet.

Frequently asked questions

What tread depth is illegal?: 2/32 of an inch in the United States and 1.6 mm in the EU and UK — the same depth expressed two ways. The moulded wear bars between the tread blocks sit at exactly that height, so when they are flush with the tread the tire is finished.
Should I replace tires at 4/32 rather than waiting for 2/32?: In wet weather, yes. Below about 4/32" the grooves no longer clear enough water and wet stopping distances grow sharply, which is why many workshops advise replacement there rather than at the legal floor.
How does the penny test compare to a gauge reading?: A penny inserted upside down hides Lincoln's head at roughly 2/32", and a quarter hides Washington's at about 4/32". They are quick checks against those two thresholds, not measurements — a gauge is what gives you a number to track.
How deep is the tread on a new tire?: Around 10/32" for a passenger tire, 11/32" for a touring all-season, 12/32" for light truck and winter tires, and 15/32" or more for all-terrain. The exact figure is usually on the manufacturer's spec sheet.
Does this predict when my tires will actually wear out?: It extrapolates the wear rate you have seen so far, which assumes the driving ahead looks like the driving behind. Rotation, pressure, alignment and how much of your mileage is motorway all shift the real answer.

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Wheel Offset Calculator — Convert wheel offset to backspacing and compare how two wheels sit on the hub.
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