Tire tread depth chart: when to replace your tires
By Tread AI team. Updated October 17, 2026
New car tires start with about 8–9 mm (10/32″–11/32″) of tread. How much you have left decides how well the tire clears water, and that is where worn tires lose grip first.
| Depth | 32nds of an inch | What it means |
|---|---|---|
| 8 mm | 10/32″ | New or nearly new |
| 6 mm | 8/32″ | Healthy; plenty of grip in rain |
| 4.5 mm | 6/32″ | Still fine; start watching it |
| 3 mm | 4/32″ | Wet braking noticeably longer; plan new tires |
| 2 mm | 3/32″ | Replace soon |
| 1.6 mm | 2/32″ | Legal minimum in most US states; replace now |
The penny and quarter tests
- Penny: put Lincoln’s head into a groove, upside down. If you can see the top of his head, you are at or below 2/32″ and need new tires.
- Quarter: do the same with Washington’s head. If you can see all of it, you are at about 4/32″ or less, the point where wet-road performance drops.
- Check several grooves across the tire. Tires rarely wear evenly.
Tread wear indicator bars
Small raised bars sit across the main grooves at 2/32″. When the tread is flush with them, the tire is at the legal limit.
What uneven wear tells you
- Both edges worn: under-inflation.
- Center worn: over-inflation.
- One edge worn: wheel alignment.
- Patchy or cupped: worn suspension or a balance problem.
Check all four in a few minutes
Tread AI measures depth from a photo of each tire, flags uneven wear, and rates every tire Good, Review or Replace using the same bands as this chart. Readings are estimates, so near the limit, confirm with a gauge or a tire shop.
Check your own tires
Depth, age and wear for all four tires, from your iPhone. Your first 2 checks are free, then $1.99 a check or go unlimited with Premium.