MM to Inches Conversion Chart
The complete metric-to-inch conversion table for machinists and DIY work: every common millimetre size in decimal inches and the nearest 64th-inch fraction, plus a reverse fraction-to-mm table and the drill-bit sizes people look up most.
MM to inches table (0.5 – 32 mm)
| Millimetres | Inches (decimal) | Nearest fraction |
|---|---|---|
| 0.5 mm | 0.0197 in | 1/64" |
| 1 mm | 0.0394 in | 3/64" |
| 1.5 mm | 0.0591 in | 1/16" |
| 1.75 mm | 0.0689 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" |
| 3.5 mm | 0.1378 in | 9/64" |
| 4 mm | 0.1575 in | 5/32" |
| 4.5 mm | 0.1772 in | 11/64" |
| 5 mm | 0.1969 in | 13/64" |
| 5.5 mm | 0.2165 in | 7/32" |
| 6 mm | 0.2362 in | 15/64" |
| 6.5 mm | 0.2559 in | 1/4" |
| 7 mm | 0.2756 in | 9/32" |
| 7.5 mm | 0.2953 in | 19/64" |
| 8 mm | 0.3150 in | 5/16" |
| 8.5 mm | 0.3346 in | 21/64" |
| 9 mm | 0.3543 in | 23/64" |
| 9.5 mm | 0.3740 in | 3/8" |
| 10 mm | 0.3937 in | 25/64" |
| 10.2 mm | 0.4016 in | 13/32" |
| 10.5 mm | 0.4134 in | 13/32" |
| 11 mm | 0.4331 in | 7/16" |
| 12 mm | 0.4724 in | 15/32" |
| 13 mm | 0.5118 in | 33/64" |
| 14 mm | 0.5512 in | 35/64" |
| 15 mm | 0.5906 in | 19/32" |
| 16 mm | 0.6299 in | 5/8" |
| 18 mm | 0.7087 in | 45/64" |
| 20 mm | 0.7874 in | 25/32" |
| 22 mm | 0.8661 in | 55/64" |
| 25 mm | 0.9843 in | 63/64" |
| 26 mm | 1.0236 in | ≈1"" |
| 28 mm | 1.1024 in | 1-7/64" |
| 30 mm | 1.1811 in | 1-3/16" |
| 32 mm | 1.2598 in | 1-1/4" |
Inches and fractions to mm
The reverse lookup — read a fractional tape-measure or bit marking and get millimetres:
| Fraction | Inches (decimal) | Millimetres |
|---|---|---|
| 1/16" | 0.0625 in | 1.5875 mm |
| 1/8" | 0.1250 in | 3.1750 mm |
| 15/64" | 0.2344 in | 5.9531 mm |
| 3/16" | 0.1875 in | 4.7625 mm |
| 1/4" | 0.2500 in | 6.3500 mm |
| 5/16" | 0.3125 in | 7.9375 mm |
| 3/8" | 0.3750 in | 9.5250 mm |
| 7/16" | 0.4375 in | 11.1125 mm |
| 1/2" | 0.5000 in | 12.7000 mm |
| 9/16" | 0.5625 in | 14.2875 mm |
| 5/8" | 0.6250 in | 15.8750 mm |
| 11/16" | 0.6875 in | 17.4625 mm |
| 3/4" | 0.7500 in | 19.0500 mm |
| 7/8" | 0.8750 in | 22.2250 mm |
| 1" | 1.0000 in | 25.4000 mm |
Common metric drill bits in inches
Metric-labelled bits are sold by millimetre size, but drills, chucks and taps in the US are marked in inches. The most-looked-up metric bits:
| Drill bit | Inches | Nearest US bit | Common use |
|---|---|---|---|
| 2.5 mm | 0.0984 in | 3/32" | M3 tap drill |
| 3 mm | 0.1181 in | 1/8" | M4 tap drill in soft material |
| 4 mm | 0.1575 in | 5/32" | M5 tap drill in soft material |
| 5 mm | 0.1969 in | 13/64" | M6 tap drill |
| 6 mm | 0.2362 in | 15/64" | M7 tap drill; M8 needs 6.8 mm |
| 8 mm | 0.3150 in | 5/16" | M9 tap drill; M10 needs 8.5 mm |
| 10 mm | 0.3937 in | 25/64" | M11 × 1.0 tap drill; M12 needs 10.2 mm |
| 10.2 mm | 0.4016 in | 13/32" | M12 × 1.75 tap drill |
| 10.5 mm | 0.4134 in | 13/32" | M12 fine-pitch tap drill |
| 12 mm | 0.4724 in | 15/32" | M14 tap drill |
Remember the metric tap-drill rule from the metric chart: drill = major − pitch. A 6 mm bit is not the M6 tap drill — the M6 tap drill is 5.0 mm.
How to convert mm to inches by hand
inches = mm ÷ 25.4 mm = inches × 25.4 quick mental math: 1 mm ≈ 0.04 in, so 6 mm ≈ 6 × 0.04 = 0.24 in reverse shortcut: 1/4 in = 6.35 mm, and each extra 1/64 in ≈ 0.40 mm
The 25.4 divisor is exact — since 1959 the inch is defined as exactly 25.4 millimetres worldwide, so conversions have no rounding ambiguity.