Length Converter
Convert length units. Exact factors, a quick reference table and worked examples.
25.4 mm = 1 in
The same value in every unit
| Unit | Symbol | Value |
|---|---|---|
| Micrometer | µm | 25 400 |
| Millimeter | mm | 25.4 |
| Centimeter | cm | 2.54 |
| Meter | m | 0.0254 |
| Kilometer | km | 2.54 × 10⁻⁵ |
| Thou (mil) | thou | 1 000 |
| Inch | in | 1 |
| Foot | ft | 0.08333333 |
| Yard | yd | 0.02777778 |
| Mile | mi | 1.57828 × 10⁻⁵ |
| Nautical mile | nmi | 1.37149 × 10⁻⁵ |
How to convert length units
Every length unit is related to one base unit (Meter, m) by an exact factor. To convert, multiply by the factor of the unit you start from and divide by the factor of the unit you want.
value in new unit = value × (factor of old unit ÷ factor of new unit)
For example, 1 mm = 0.001 m and 1 in = 0.0254 m, so 1 mm = 0.03937008 in.
Quick reference table
How many of the units in the column headings make up one of the unit in each row.
| One… | = µm | = mm | = cm | = m | = km | = thou |
|---|---|---|---|---|---|---|
| 1 µm | 1 | 0.001 | 1 × 10⁻⁴ | 1 × 10⁻⁶ | 1 × 10⁻⁹ | 0.03937008 |
| 1 mm | 1 000 | 1 | 0.1 | 0.001 | 1 × 10⁻⁶ | 39.37008 |
| 1 cm | 10 000 | 10 | 1 | 0.01 | 1 × 10⁻⁵ | 393.7008 |
| 1 m | 1 000 000 | 1 000 | 100 | 1 | 0.001 | 39 370.08 |
| 1 km | 1 × 10⁹ | 1 000 000 | 100 000 | 1 000 | 1 | 39 370 079 |
| 1 thou | 25.4 | 0.0254 | 0.00254 | 2.54 × 10⁻⁵ | 2.54 × 10⁻⁸ | 1 |
| 1 in | 25 400 | 25.4 | 2.54 | 0.0254 | 2.54 × 10⁻⁵ | 1 000 |
| 1 ft | 304 800 | 304.8 | 30.48 | 0.3048 | 0.0003048 | 12 000 |
| 1 yd | 914 400 | 914.4 | 91.44 | 0.9144 | 0.0009144 | 36 000 |
| 1 mi | 1.60934 × 10⁹ | 1 609 344 | 160 934.4 | 1 609.344 | 1.609344 | 63 360 000 |
| 1 nmi | 1.852 × 10⁹ | 1 852 000 | 185 200 | 1 852 | 1.852 | 72 913 386 |
Common values: mm to in
| Millimeter (mm) | Inch (in) |
|---|---|
| 1 mm | 0.03937008 in |
| 2 mm | 0.07874016 in |
| 5 mm | 0.1968504 in |
| 10 mm | 0.3937008 in |
| 20 mm | 0.7874016 in |
| 50 mm | 1.968504 in |
| 100 mm | 3.937008 in |
| 200 mm | 7.874016 in |
| 500 mm | 19.68504 in |
| 1 000 mm | 39.37008 in |
Worked examples
Convert 25.4 mm to in
- 1 mm = 0.001 m and 1 in = 0.0254 m.
- 25.4 × 0.001 ÷ 0.0254 = 1 in.
Convert 50 cm to µm
- 1 cm = 0.01 m and 1 µm = 1 × 10⁻⁶ m.
- 50 × 0.01 ÷ 1 × 10⁻⁶ = 500 000 µm.
Convert 250 nmi to mm
- 1 nmi = 1 852 m and 1 mm = 0.001 m.
- 250 × 1 852 ÷ 0.001 = 463 000 000 mm.
The units explained
| Unit | Symbol | Exact factor | Where it is used |
|---|---|---|---|
| Micrometer | µm | 1 µm = 1 × 10⁻⁶ m | Surface finish, tolerances |
| Millimeter | mm | 1 mm = 0.001 m | Machining, drawings |
| Centimeter | cm | 1 cm = 0.01 m | Everyday sizes |
| Meter | m | 1 m = 1 m | SI unit |
| Kilometer | km | 1 km = 1 000 m | Distances |
| Thou (mil) | thou | 1 thou = 2.54 × 10⁻⁵ m | US tolerances, coatings |
| Inch | in | 1 in = 0.0254 m | US machining and drawings |
| Foot | ft | 1 ft = 0.3048 m | US building, aviation |
| Yard | yd | 1 yd = 0.9144 m | Textiles, sports |
| Mile | mi | 1 mi = 1 609.344 m | Road distances (US, UK) |
| Nautical mile | nmi | 1 nmi = 1 852 m | Sea and air navigation |
Key facts
- 1 inch = 25.4 mm exactly. 1 foot = 0.3048 m exactly.
- 1 thou (mil) = 0.001 in = 0.0254 mm.
Related converters, guides and tools
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FAQ
How many Inch units are in one Millimeter?
1 mm = 0.03937008 in.
How do I convert mm to in?
Multiply by 0.03937008 (the factor 0.001 ÷ 0.0254). To go back, divide by 0.03937008 or multiply by 25.4.
What is the micrometer (µm) used for?
Surface finish, tolerances.
What is the millimeter (mm) used for?
Machining, drawings.
Are the conversion factors exact?
Where a unit is defined exactly (the inch is 25.4 mm, the pound is 0.45359237 kg, standard gravity is 9.80665 m/s²) the factor is exact; others are given to ten or more digits. Results are shown to seven significant digits.
References
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), and NIST Handbook 44, Appendix C (general tables of units of measurement).
- BIPM, The International System of Units (SI Brochure), 9th edition; ISO 80000 (quantities and units).
Last reviewed: November 2026.