Millimetres to inches converter
Drawing sets moving between metric and imperial offices are the single most common source of dimension errors in CAD. One inch is exactly 25.4 mm — the conversion is defined, not measured — so the only real risk is rounding. This converter shows the exact decimal value plus the nearest 1/16in fraction that US construction documents normally use.
mm to inches converter
- Inches
- 39.3701in
- Nearest 1/16 inch
- 39 3/8"
- Feet and inches
- 3' 3.37"
- Centimetres
- 100cm
Formula
inches = millimetres ÷ 25.425.4 is exact by international definition (1959 international yard and pound agreement), so no precision is lost in the conversion itself.
Worked examples
| Input | Result |
|---|---|
| 2400 mm door height | 94.4882 in ≈ 7'-10 1/2" |
| 300 mm module | 11.811 in ≈ 11 13/16" |
| 12 mm plasterboard | 0.4724 in ≈ 15/32" |
mm to inches — common drawing values
Exact decimal inches plus the nearest 1/16 in fraction used on US construction documents.
| Millimetres | Inches |
|---|---|
| 1 mm | 0.0394 in ≈ 0 1/16" |
| 2 mm | 0.0787 in ≈ 0 1/16" |
| 3 mm | 0.1181 in ≈ 0 1/8" |
| 5 mm | 0.1969 in ≈ 0 3/16" |
| 6 mm | 0.2362 in ≈ 0 1/4" |
| 8 mm | 0.315 in ≈ 0 5/16" |
| 10 mm | 0.3937 in ≈ 0 3/8" |
| 12 mm | 0.4724 in ≈ 0 1/2" |
| 15 mm | 0.5906 in ≈ 0 9/16" |
| 16 mm | 0.6299 in ≈ 0 5/8" |
| 19 mm | 0.748 in ≈ 0 3/4" |
| 20 mm | 0.7874 in ≈ 0 13/16" |
| 25 mm | 0.9843 in ≈ 1" |
| 30 mm | 1.1811 in ≈ 1 3/16" |
| 40 mm | 1.5748 in ≈ 1 9/16" |
| 50 mm | 1.9685 in ≈ 1 15/16" |
| 75 mm | 2.9528 in ≈ 2 15/16" |
| 100 mm | 3.937 in ≈ 3 15/16" |
| 150 mm | 5.9055 in ≈ 5 7/8" |
| 200 mm | 7.874 in ≈ 7 7/8" |
| 250 mm | 9.8425 in ≈ 9 13/16" |
| 300 mm | 11.811 in ≈ 11 13/16" |
| 500 mm | 19.685 in ≈ 19 11/16" |
| 1,000 mm | 39.3701 in ≈ 39 3/8" |
Questions
How many millimetres are in an inch?
Exactly 25.4 mm. It is a defined value, not a measurement, so 1 in = 25.4 mm holds at any precision.
Should I round metric dimensions to whole inches on a drawing?
No. Round to the nearest 1/16 in on architectural sheets and to three decimal places on machined parts. Rounding a 2400 mm dimension to 94 in loses almost 12 mm — enough to break a door schedule.
How do I set inches in a metric AutoCAD drawing?
Leave the model in millimetres and change only the dimension style: set DIMLFAC to 1/25.4 (0.03937) on an inch-annotated layout, or use a separate imperial dimension style. Rescaling the geometry itself is what corrupts coordinated models.
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