How to convert millimeters to inches
Every millimeter is 0.03937 inches, so the conversion is a single multiplication:
Worked example: 25 mm → 25 × 0.0393701 = 0.9843 in.
Quick mental estimate: Divide by 25: 25 ÷ 25 ≈ 1 in (exact: 0.9843).
Millimeters to inches conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.1181 in |
| 5 mm | 0.1969 in |
| 10 mm | 0.3937 in |
| 15 mm | 0.5906 in |
| 20 mm | 0.7874 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 75 mm | 2.9528 in |
| 100 mm | 3.937 in |
| 200 mm | 7.874 in |
| 250 mm | 9.8425 in |
| 500 mm | 19.6851 in |
| 1,000 mm | 39.3701 in |
Values rounded to four decimals. For a value that is not in the table, use the converter above — it accepts decimals and negative numbers.
When you need this conversion
- Buying anything sized abroad: screens, bike frames, luggage limits and clothing patterns switch between metric and imperial depending on where they were made.
- DIY and construction: timber, pipe diameters and fixings are stocked in one system or the other, and a plan drawn in one has to be ordered in the second.
- Travel and sport: race distances, altitudes and road signs change unit at almost every border.
Getting it right
The arithmetic is a single multiplication, so mistakes almost never come from the calculation itself — they come from the value that goes into it. Check that the figure you are converting really is in millimeters and not in a neighbouring unit, and that you have not already converted it once.
Sanity-check the direction of the result before you use it. One millimeter is 0.03937 inches, so converting millimeters to inches should make the number smaller. If it moved the other way, the conversion was applied backwards — the reverse converter is one click away.
About the units
Millimeter (mm)
The millimeter is one thousandth of a meter. Engineering drawings, machine parts, rainfall and screen sizes are specified in millimeters because the unit is fine enough to avoid decimals.
Inch (in)
The inch is one twelfth of a foot, fixed at exactly 2.54 centimeters by international agreement in 1959. Screens, paper, pipes and construction lumber in the US are all sized in inches.
Frequently asked questions
How many inches are in 1 millimeter?
1 millimeter equals 0.03937 inches. To convert any value, multiply the number of millimeters by 0.0393701.
How do I convert millimeters to inches in my head?
Divide by 25: 25 ÷ 25 ≈ 1 in (exact: 0.9843).
Is the mm to in conversion exact?
1 inch is exactly 25.4 mm, so the factor 0.0393701 is 1 ÷ 25.4 rounded.
How do I convert millimeters to inches in Excel or Google Sheets?
Put the value in A1 and use =A1*0.0393701. Both Excel and Google Sheets also have a built-in function, =CONVERT(A1,"mm","in"), which avoids typing the factor by hand.
How many decimal places should I keep?
For everyday use two decimals are plenty. Keep four if the result feeds another calculation, and round only at the very end — rounding intermediate steps is the most common reason a result comes out slightly wrong.