Metric to US Conversion Table for common fastener sizes
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Below is a single, consolidated reference for comparing common metric diameters or lengths (in mm) with their approximate inch equivalents (“in.”) and the closest common fraction typically used by mechanics. If you see a fastener labeled “M6,” that simply refers to 6 mm.
| Metric (mm) | Inches (in.) | Closest Fraction* |
|---|---|---|
| 1.5 mm | 0.059 in. | 1/16" |
| 2 mm | 0.0787 in. | 5/64" |
| 2.5 mm | 0.0984 in. | 3/32" |
| 3 mm | 0.1181 in. | 1/8" |
| 4 mm | 0.1575 in. | 5/32" |
| 5 mm | 0.1969 in. | 3/16" |
| 6 mm | 0.2362 in. | 1/4" |
| 8 mm | 0.3150 in. | 5/16" |
| 10 mm | 0.3937 in. | 13/32" |
| 12 mm | 0.4724 in. | 15/32" |
| 14 mm | 0.5512 in. | 9/16" |
| 15 mm | 0.5906 in. | 19/32" |
| 16 mm | 0.6299 in. | 5/8" |
| 18 mm | 0.7087 in. | 11/16" |
| 20 mm | 0.7874 in. | 25/32" |
| 22 mm | 0.8661 in. | 7/8" |
| 25 mm | 0.9843 in. | 1" |
| 28 mm | 1.1024 in. | 1-1/8" |
| 30 mm | 1.1811 in. | 1-3/16" |
| 35 mm | 1.3780 in. | 1-3/8" |
| 40 mm | 1.5748 in. | 1-9/16" |
| 45 mm | 1.7717 in. | 1-3/4" |
| 50 mm | 1.9685 in. | 2" (approx.) |
| 55 mm | 2.1654 in. | 2-1/8" |
| 60 mm | 2.3622 in. | 2-3/8" |
| 65 mm | 2.5591 in. | 2-9/16" |
| 70 mm | 2.7559 in. | 2-3/4" |
| 75 mm | 2.9528 in. | 2-15/16" |
| 80 mm | 3.1496 in. | 3-1/8" |
| 85 mm | 3.3465 in. | 3-5/16" |
| 90 mm | 3.5433 in. | 3-1/2" |
| 95 mm | 3.7402 in. | 3-3/4" |
| 100 mm | 3.9370 in. | 3-15/16" |
| 110 mm | 4.3307 in. | 4-5/16" |
| 120 mm | 4.7244 in. | 4-3/4" |
| 125 mm | 4.9213 in. | 5" (approx.) |
| 130 mm | 5.1181 in. | 5-1/8" |
| 140 mm | 5.5118 in. | 5-1/2" |
| 150 mm | 5.9055 in. | 6" (approx.) |
| 160 mm | 6.2992 in. | 6-5/16" |
| 170 mm | 6.6929 in. | 6-11/16" |
| 175 mm | 6.8898 in. | 6-7/8" |
| 180 mm | 7.0866 in. | 7-1/16" |
| 190 mm | 7.4803 in. | 7-1/2" |
| 200 mm | 7.8740 in. | 7-7/8" |
* Common mechanical fraction approximations—some values lie between fractions but we've rounded to more familiar ones for wrenches and sockets.
Tip: If a screw is labeled “M4,” it simply refers to a diameter of 4 mm. The length is also often measured in millimeters, such as M4 x 16 for 4 mm diameter by 16 mm long.