Tread Depth Unit Converter
Switch tread depth between mm and 32nds. Use the calculator below. Results update as you type.
How the Tread Depth Unit Converter Works
This converter works by converting tread depth between 32nds of an inch, decimal inches and millimeters. US gauges read in 32nds; most other countries use millimeters.
- Enter a depth, for example 4/32 in.
- Read the decimal inches: 0.1250 in.
- Read the millimeters: 3.2 mm.
- Enter a millimeter value instead, for example 1.6 mm, to get 2/32 in.
The Formula
The formula is Depth (mm) = (32nds ÷ 32) × 25.4.
Depth (in) = 32nds ÷ 32 Depth (mm) = 32nds ÷ 32 × 25.4 = 32nds × 0.79375 32nds = Depth (mm) ÷ 0.79375Each 1/32 in equals 0.794 mm. Worked example: 10/32 in is 0.3125 in, or 7.9 mm.
Conversion Table
The conversion table converts 14 tread depths from 2/32 in to 18/32 in into decimal inches and millimeters. New passenger tires start near 10/32–11/32 in (7.9–8.7 mm); new LT and mud-terrain tires start near 14/32–18/32 in (11.1–14.3 mm).
The note under the table gives the common legal minimums: 2/32 in in the US and 1.6 mm in the EU.
| 32nds | Inches | Millimeters |
|---|---|---|
| 2/32 | 0.0625 | 1.6 |
| 3/32 | 0.0938 | 2.4 |
| 4/32 | 0.1250 | 3.2 |
| 5/32 | 0.1562 | 4.0 |
| 6/32 | 0.1875 | 4.8 |
| 7/32 | 0.2188 | 5.6 |
| 8/32 | 0.2500 | 6.3 |
| 9/32 | 0.2812 | 7.1 |
| 10/32 | 0.3125 | 7.9 |
| 11/32 | 0.3438 | 8.7 |
| 12/32 | 0.3750 | 9.5 |
| 14/32 | 0.4375 | 11.1 |
| 16/32 | 0.5000 | 12.7 |
| 18/32 | 0.5625 | 14.3 |
2/32 in (1.6 mm) is the common legal minimum in the US; 1.6 mm is the EU minimum for cars.
What Is the Tread Depth Unit Converter?
The Tread Depth Unit Converter is a tool that translates tread depth between the US 32nds system and metric millimeters. Tread depth decides wet grip, snow grip and legal roadworthiness.
Spec sheets from global tire makers list new tread depth in both units. Inspection rules use the local unit. The converter lines them up.
Common Uses
This converter has 4 uses: legal checks, spec comparison, wear tracking and AWD matching.
- Check legal minimums: Compare a reading with local rules.
- Compare specs: Line up tread depths across brands.
- Track wear: Log readings in one unit.
- Match AWD tires: Convert tread gaps for the AWD tool.