How to check tire tread depth

Measure the main grooves with a tread depth gauge, and replace the tire when the tread is flush with the wear bars at about 1.6 mm (2/32 inch).

Updated 2026-10-27

What you are measuring

Tread depth is the depth of the main grooves, from the wear surface down to the base of the groove. Measure in those grooves. Do not measure on top of a wear indicator bar, and do not measure a tie bar or a stone ejector. Those sit higher and will make the tire look more worn than it is, or less, depending on where you land.

Use a gauge, and check more than one spot

A tread depth gauge reads millimetres or 32nds of an inch. Push the probe into a main groove until the gauge’s shoulders sit on the tread blocks, then read it. A coin is only a rough check. The gauge is the measurement.

Check several grooves across the tread, and check the inside, middle, and outside. Then check the other tires. A tire can be legal in the centre and worn out on a shoulder.

The wear bars are the comparison that does not need a tool. They are the narrow bars running across the groove. At about 1.6 mm (2/32 inch), the bar becomes flush with the tread. That tire is done.

What uneven numbers mean

If one side of a tire is much shallower than the other, the tire may still have to come off even though the deep side looks fine. The shallow side is the one in contact with the road in a corner. Have inflation and alignment checked so the next tire does not wear the same way.

For winter tires, do not treat 1.6 mm as a snow-ready depth. Many makers suggest replacing a winter tire around 4/32 inch (3.2 mm) because snow traction drops before the wear bars.