Millimeters to Inches Converter
Convert millimeters to inches instantly with reference table.
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1 mm = 0.03937007874 in
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.03937007874 |
| 2 | 0.07874015748 |
| 5 | 0.1968503937 |
| 10 | 0.3937007874 |
| 15 | 0.5905511811 |
| 20 | 0.7874015748 |
| 25 | 0.9842519685 |
| 50 | 1.968503937 |
| 75 | 2.952755906 |
| 100 | 3.937007874 |
| 150 | 5.905511811 |
| 200 | 7.874015748 |
| 250 | 9.842519685 |
| 500 | 19.68503937 |
| 1,000 | 39.37007874 |
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How to Convert Millimeters to Inches
Formula: inches = mm × 0.03937 (or mm ÷ 25.4)
Since 1 inch = 25.4 mm exactly, dividing by 25.4 gives the precise conversion.
| Millimeters | Inches (decimal) | Approx. Fraction |
|---|---|---|
| 1 mm | 0.039" | ~1/25" |
| 2 mm | 0.079" | ~5/64" |
| 3 mm | 0.118" | ~1/8" |
| 4 mm | 0.157" | ~5/32" |
| 5 mm | 0.197" | ~13/64" |
| 6 mm | 0.236" | ~15/64" |
| 7 mm | 0.276" | ~9/32" |
| 8 mm | 0.315" | ~5/16" |
| 9 mm | 0.354" | ~23/64" |
| 10 mm | 0.394" | ~25/64" |
| 11 mm | 0.433" | ~7/16" |
| 12 mm | 0.472" | ~15/32" |
| 13 mm | 0.512" | ~1/2" |
| 14 mm | 0.551" | ~35/64" |
| 15 mm | 0.591" | ~19/32" |
| 16 mm | 0.630" | ~5/8" |
| 17 mm | 0.669" | ~43/64" |
| 18 mm | 0.709" | ~45/64" |
| 19 mm | 0.748" | ~3/4" |
| 20 mm | 0.787" | ~25/32" |
| 21 mm | 0.827" | ~53/64" |
| 22 mm | 0.866" | ~7/8" |
| 23 mm | 0.906" | ~29/32" |
| 24 mm | 0.945" | ~15/16" |
| 25 mm | 0.984" | ~1" |
| 30 mm | 1.181" | ~1 3/16" |
| 40 mm | 1.575" | ~1 37/64" |
| 50 mm | 1.969" | ~2" |
| 75 mm | 2.953" | ~3" |
| 100 mm | 3.937" | ~4" |
When You Need This Conversion
Engineering and machining: Technical drawings often specify tolerances in millimeters. Converting to inches is necessary when using imperial measurement tools.
Jewelry: Ring band widths and gemstone sizes are typically specified in millimeters. A 6mm ring band is about 1/4 inch wide.
3D printing: Layer heights and nozzle diameters are in millimeters (0.2 mm layer height = 0.008 inches). Wrench and socket sizes also frequently cross between mm and inches.
For all length conversions, see our Length Converter.
When to use this
You are ordering a machine part from a metric-country supplier and the specs say 12.7 mm — is that going to fit your half-inch socket? Or you are buying jewelry and the band width is listed as 6 mm and you want to visualize that in inches. Millimeter-to-inch conversion is critical in engineering, manufacturing, 3D printing, jewelry, and any precision work where small measurements cross between metric and imperial systems.
The formula is simple: divide millimeters by 25.4 to get inches. One inch equals exactly 25.4 mm — this is the international standard. So 10 mm is 0.3937 inches, 25.4 mm is exactly 1 inch, and 50 mm is 1.9685 inches. At this scale, even small rounding errors can matter, so the converter carries enough decimal places for precision work.
Good to know
25.4 mm per inch is exact. This is a defined relationship, not a measured one. Every mm-to-inches conversion is mathematically precise — the only question is how many decimal places you need for your application. For woodworking, two decimal places are fine. For machining, you may need four or more.
Wrench and socket sizes straddle both systems. A 13 mm wrench is close to but not exactly 1/2 inch (12.7 mm). A 10 mm socket is near 3/8 inch (9.525 mm). Using metric wrenches on imperial bolts (or vice versa) can round off bolt heads. Knowing the exact mm equivalents of common fractional-inch sizes prevents stripped hardware.
Rainfall is measured in millimeters in most countries. When a weather report says 25 mm of rain fell, that is about 1 inch. Light rain is 1–2 mm/hr, moderate is 2–8 mm/hr, and heavy is above 8 mm/hr. Knowing the inch equivalents makes international weather reports more intuitive.
Quick Reference
| Millimeters | Inches | Fractional Inch (nearest) |
|---|---|---|
| 1 mm | 0.039 in | ~1/32" |
| 2 mm | 0.079 in | ~5/64" |
| 3 mm | 0.118 in | ~1/8" |
| 5 mm | 0.197 in | ~3/16" |
| 6.35 mm | 0.250 in | 1/4" (exact) |
| 8 mm | 0.315 in | ~5/16" |
| 10 mm | 0.394 in | ~3/8" |
| 12.7 mm | 0.500 in | 1/2" (exact) |
| 15 mm | 0.591 in | ~19/32" |
| 19.05 mm | 0.750 in | 3/4" (exact) |
| 25.4 mm | 1.000 in | 1" (exact) |
| 50.8 mm | 2.000 in | 2" (exact) |