Enter a measurement in millimeters to convert it to 32nds of an inch, or enter a value in 32nds to convert back. The most common use is tire tread depth: US tires are rated in 32nds while many gauges and European specs report in millimeters.
| Millimeters to 32nds | 32nds to Millimeters |
|---|---|
| 1 mm = 1.2598 32nds | 1 32nd = 0.7938 mm |
| 2 mm = 2.5197 32nds | 2 32nds = 1.5875 mm |
| 3 mm = 3.7795 32nds | 3 32nds = 2.3813 mm |
| 4 mm = 5.0394 32nds | 4 32nds = 3.1750 mm |
| 5 mm = 6.2992 32nds | 5 32nds = 3.9688 mm |
| 6 mm = 7.5591 32nds | 6 32nds = 4.7625 mm |
| 8 mm = 10.0787 32nds | 7 32nds = 5.5563 mm |
| 10 mm = 12.5984 32nds | 8 32nds = 6.3500 mm |
| 12 mm = 15.1181 32nds | 10 32nds = 7.9375 mm |
| 15 mm = 18.8976 32nds | 12 32nds = 9.5250 mm |
| 16 mm = 20.1575 32nds | 14 32nds = 11.1125 mm |
| 18 mm = 22.6772 32nds | 16 32nds = 12.7000 mm |
| 19 mm = 23.9370 32nds | 18 32nds = 14.2875 mm |
| 20 mm = 25.1969 32nds | 20 32nds = 15.8750 mm |
| 22 mm = 27.7165 32nds | 24 32nds = 19.0500 mm |
| 25 mm = 31.4961 32nds | 28 32nds = 22.2250 mm |
| 30 mm = 37.7953 32nds | 32 32nds = 25.4000 mm |
| 32 mm = 40.3150 32nds | 40 32nds = 31.7500 mm |
| 40 mm = 50.3937 32nds | 48 32nds = 38.1000 mm |
| 50 mm = 62.9921 32nds | 64 32nds = 50.8000 mm |
| Formula: 32nds = mm × 32 ÷ 25.4 | mm = 32nds × 25.4 ÷ 32 | |
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Mm To 32Nds Formula
The exact formula for converting millimeters to 32nds of an inch is derived from the definition of the inch (1 inch = 25.4 mm exactly) divided into 32 equal parts:
32N = Mm × (32 ÷ 25.4) = Mm × 1.25984
Variables:
- 32N is the measurement in 32nds of an inch
- Mm is the measurement in millimeters
The reverse formula is: Mm = 32N × 25.4 ÷ 32 = 32N × 0.79375. Each 32nd of an inch is exactly 0.79375 mm. Note: the commonly cited approximation of × 1.27 introduces a ~0.8% error because it assumes 1 inch = 25.2 mm rather than the standard 25.4 mm.
What Are 32nds of an Inch?
A 32nd of an inch (1/32″) equals exactly 0.79375 mm. The unit divides one inch into 32 equal parts, providing a measurement granularity fine enough to detect meaningful differences while remaining coarse enough to read without precision instruments. Today the unit is used almost exclusively for tire tread depth in the United States, where it became the standard because tire gauges were calibrated in imperial fractions before the US adopted metric in other trades. The EU uses millimeters for the same measurement but sets the same legal minimum: 1.6 mm = 2/32″.
Tire Tread Depth Reference: 32nds vs mm
The table below maps tread depth thresholds published by US safety research and tire manufacturers. New passenger car tires ship at 10/32″ to 11/32″; light truck and SUV tires at 11/32″ to 13/32″; off-road tires up to 19/32″.
| Tread Depth (32nds) | Tread Depth (mm) | Status |
|---|---|---|
| 13/32″ or more | 10.3 mm+ | New (off-road / truck tires) |
| 10/32″ to 11/32″ | 7.9 to 8.7 mm | New (passenger car tires) |
| 8/32″ | 6.4 mm | Good; full wet-weather performance |
| 6/32″ | 4.8 mm | Acceptable; recommended minimum for winter driving |
| 4/32″ | 3.2 mm | Caution: wet-weather braking begins to degrade; research shows up to 50% friction loss vs new tire on wet roads at highway speed |
| 3/32″ | 2.4 mm | Replace soon; quarter test positive (Washington’s head visible) |
| 2/32″ | 1.6 mm | US legal minimum (most states); EU legal minimum; replace immediately. Penny test positive (Lincoln’s head visible). |
| Sources: NHTSA, Michelin, Bridgestone; most US states set the legal minimum at 2/32″ (1.6 mm) for passenger tires. | ||
