Tire tread depth calculator
Enter the tread depth when new and the depth now, in 32nds of an inch, to see how much tread is left before the wear bars and how much of the usable tread you have used.
| Tread left above the wear bars | 4.0/32 in | 3.2 mm |
|---|---|---|
| Tread worn since new | 50% | |
| Usable tread left | 40% | new depth minus 2/32 |
| Estimated miles left at the same rate | 20,000 | estimate only |
When to replace
Every new radial tire for US light vehicles (up to 10,000 lb GVWR) has at least six tread wear indicators, raised bars across the grooves, that show when the tread is down to 1/16 in (2/32 in) (FMVSS No. 139 S5.4). NHTSA says tires are not safe and should be replaced when the tread is worn down to 2/32 in, and suggests checking the tread at least once a month when you check the pressure.
The penny test
NHTSA describes a quick check: put a penny in the tread with Lincoln's head upside down and facing you. If you can see the top of Lincoln's head, replace the tire. A tread depth gauge gives a number you can enter above. See how to check tread depth.
32nds, inches and millimeters
| 32nds | Inches | mm | Note |
|---|---|---|---|
| 12/32 | 0.375 | 9.5 | |
| 11/32 | 0.344 | 8.7 | |
| 10/32 | 0.312 | 7.9 | |
| 9/32 | 0.281 | 7.1 | |
| 8/32 | 0.250 | 6.3 | |
| 7/32 | 0.219 | 5.6 | |
| 6/32 | 0.188 | 4.8 | |
| 5/32 | 0.156 | 4.0 | |
| 4/32 | 0.125 | 3.2 | |
| 3/32 | 0.094 | 2.4 | |
| 2/32 | 0.062 | 1.6 | Wear bars: replace |
| 1/32 | 0.031 | 0.8 | Below the wear bars |
Limits of this calculator
The miles-left figure assumes the tire keeps wearing at the same rate, which is rarely true; alignment, pressure, load and driving change it. Measure several grooves and use the lowest reading. State laws on minimum tread depth vary; check your state's rule.
Printed from https://tiresizecalc.net/tread-depth-calculator/. Figures as published on 2026-11-01. The full working and the official sources are on that page.
Sources
- 49 CFR 571.139 - Standard No. 139; New pneumatic radial tires for light vehicles. National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations (eCFR). 49 CFR 571.139. eCFR up to date as of 2026-10-15. S5.4: treadwear indicators at 1/16 in (2/32 in). Retrieved 2026-11-01.
- Tires (Tire Safety). National Highway Traffic Safety Administration (NHTSA). Undated web page. Tread depth: replace at 2/32 in; penny test; monthly check. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Tread left = current - 2/32; percent of usable tread = (current - 2) / (new - 2); miles left = miles / (new - current) x tread left, rounded to 100. Retrieved 2026-11-01.
Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.