Calculator
Unit conversion
Equivalent quantities with the calculation shown below.
Equivalent values
| Unit | Value |
|---|---|
| Millimetre (mm) | 1,000,000 |
| Centimetre (cm) | 100,000 |
| Metre (m) | 1,000 |
| Kilometre (km) | 1 |
| Inch (in) | 39,370.0787402 |
| Foot (ft) | 3,280.83989501 |
| International mile (mi) | 0.621371192237 |
Put dimensions into a common unit first
A 1.25 km cable route and a 350 mm installation detail cannot be added directly. Convert both to metres before using a formula. Multiply by the source unit’s metre factor, then divide by the destination unit’s factor. The reverse uses the same method. In cable calculations, check whether the entered route is one way and whether the formula already includes the return path.
Which foot, inch or mile is specified?
The foot here is the international foot: 1 ft = 0.3048 m. An inch is 25.4 mm and an international land mile is 1609.344 m. A nautical mile and the former US survey foot have different definitions. Confirm which mile your document uses. Nominal pipe sizes, such as 1/2 inch, are size designations; do not use the converted number as a measured diameter without the applicable pipe dimension table.
Area and volume need squared or cubed factors
A length conversion changes one dimension. Area uses the square of that factor, while volume uses its cube. Although 1 m = 100 cm, 1 m² = 10 000 cm². A 600 × 400 mm duct becomes 0.6 × 0.4 m, giving a cross-sectional area of 0.24 m². Converting each side before multiplying helps avoid a common error.
Worked examples
Cable route
1.25 km × 1000 = 1250 m. Entering 1.25 in a calculator expecting metres understates the route by a factor of one thousand.
Installation height
8 ft × 0.3048 = 2.4384 m. A drawing dimensioned in millimetres would show 2438.4 mm.
Duct dimensions
600 mm = 0.6 m and 400 mm = 0.4 m. Their product is 0.24 m² of cross-sectional area.
Definitions and calculation method
Unit factors and temperature-scale relationships: NIST SP 811, Appendix B.8 ↗.
Application examples were prepared for this page. Values are converted through the reference unit before display rounding; displayed results use up to 12 significant digits. A converted reading retains the uncertainty of the original measurement.