Convert mm ↔ inches instantly with accurate formulas and configurable rounding. Useful for MEP coordination, shop drawings, fabrication dimensions, and mixed-unit project documentation. Supports fraction inputs for inches (e.g., 3/8, 1 1/2).
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Construction and MEP projects often mix metric and imperial drawings. A duct detail might be shown in inches while a piping takeoff is in millimeters. This converter helps you move between mm and inches with consistent rounding—so coordination stays clean and shop fabrication matches the intent.
Rounding depends on what you’re doing:
| Millimeters (mm) | Inches (decimal) | Nearest 1/16 in |
|---|---|---|
| 1 mm | 0.0394 | 1/16" |
| 2 mm | 0.0787 | 1/16" |
| 3 mm | 0.1181 | 1/8" |
| 4 mm | 0.1575 | 3/16" |
| 5 mm | 0.1969 | 3/16" |
| 6 mm | 0.2362 | 1/4" |
| 8 mm | 0.3150 | 5/16" |
| 9.525 mm | 0.3750 | 3/8" |
| 10 mm | 0.3937 | 3/8" |
| 12 mm | 0.4724 | 1/2" |
| 12.7 mm | 0.5000 | 1/2" |
| 15 mm | 0.5906 | 9/16" |
| 16 mm | 0.6299 | 5/8" |
| 19.05 mm | 0.7500 | 3/4" |
| 20 mm | 0.7874 | 13/16" |
| 25 mm | 0.9843 | 1" |
| 25.4 mm | 1.0000 | 1" |
| 30 mm | 1.1811 | 1 3/16" |
| 32 mm | 1.2598 | 1 1/4" |
| 38.1 mm | 1.5000 | 1 1/2" |
| 40 mm | 1.5748 | 1 9/16" |
| 50 mm | 1.9685 | 1 15/16" |
| 50.8 mm | 2.0000 | 2" |
| 63.5 mm | 2.5000 | 2 1/2" |
| 65 mm | 2.5591 | 2 9/16" |
| 75 mm | 2.9528 | 2 15/16" |
| 76.2 mm | 3.0000 | 3" |
| 80 mm | 3.1496 | 3 1/8" |
| 100 mm | 3.9370 | 3 15/16" |
| 101.6 mm | 4.0000 | 4" |
| 125 mm | 4.9213 | 4 15/16" |
| 150 mm | 5.9055 | 5 7/8" |
| 152.4 mm | 6.0000 | 6" |
| 200 mm | 7.8740 | 7 7/8" |
| 203.2 mm | 8.0000 | 8" |
| 250 mm | 9.8425 | 9 13/16" |
| 300 mm | 11.8110 | 11 13/16" |
| 305 mm | 12.0079 | 12" |
| 400 mm | 15.7480 | 15 3/4" |
| 500 mm | 19.6850 | 19 11/16" |
| 600 mm | 23.6220 | 23 5/8" |
| 610 mm | 24.0157 | 24" |
| 1000 mm | 39.3701 | 39 3/8" |
| Inches (fraction) | Inches (decimal) | Millimeters (mm) |
|---|---|---|
| 1/16" | 0.0625 | 1.5875 |
| 1/8" | 0.125 | 3.175 |
| 3/16" | 0.1875 | 4.7625 |
| 1/4" | 0.25 | 6.35 |
| 5/16" | 0.3125 | 7.9375 |
| 3/8" | 0.375 | 9.525 |
| 7/16" | 0.4375 | 11.1125 |
| 1/2" | 0.5 | 12.7 |
| 9/16" | 0.5625 | 14.2875 |
| 5/8" | 0.625 | 15.875 |
| 11/16" | 0.6875 | 17.4625 |
| 3/4" | 0.75 | 19.05 |
| 13/16" | 0.8125 | 20.6375 |
| 7/8" | 0.875 | 22.225 |
| 15/16" | 0.9375 | 23.8125 |
| 1" | 1 | 25.4 |
| 1 1/4" | 1.25 | 31.75 |
| 1 1/2" | 1.5 | 38.1 |
| 2" | 2 | 50.8 |
| 2 1/2" | 2.5 | 63.5 |
| 3" | 3 | 76.2 |
| 4" | 4 | 101.6 |
| 6" | 6 | 152.4 |
| 8" | 8 | 203.2 |
| 10" | 10 | 254 |
| 12" | 12 | 304.8 |
These quick rules help you sanity-check conversions without a calculator:
Yes. The inch is defined exactly as 25.4 millimeters, so mm to inches is mm ÷ 25.4 and inches to mm is inches × 25.4.
305 mm = 12.008 inches, which is 12 inches to the nearest 1/16 inch. 305 mm is the common metric equivalent of a 12 inch (one foot) dimension; exactly 12 inches is 304.8 mm.
They are exact inch sizes: 152.4 mm = 6 in, 38.1 mm = 1 1/2 in and 9.525 mm = 3/8 in.
Differences usually come from rounding. This tool shows the exact value, the rounded value and the nearest 1/16 inch fraction.
Yes. Inch input accepts 3/8, 1 1/2 and 1-1/2.
Drawings: 2 dp. Coordination: 3 dp. Precision: 4–6 dp.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
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