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 (in) | Notes |
|---|---|---|
| 10 | 0.3937 | Small fittings / details |
| 25.4 | 1 | Exact |
| 50 | 1.9685 | Approx 2 inches |
| 100 | 3.9370 | Approx 4 inches |
| 150 | 5.9055 | Approx 6 inches |
| 200 | 7.8740 | Approx 8 inches |
These quick rules help you sanity-check conversions without a calculator:
Yes. The inch is defined exactly as 25.4 millimeters.
Differences usually come from rounding and formatting. This tool shows both rounded and exact values.
Yes. Inch input supports fractions: 3/8, 1 1/2, and similar.
Drawings: 2 dp. Coordination: 3 dp. Precision: 4–6 dp.
Yes—nearest 1/16, 1/32, etc. can be added as an option.