Length converter
Convert any length via the SI metre. Factors are exact international definitions — see the arithmetic for your input, plus a table of every equivalent.
Defaults to your region. Switch to compare any other scale.
Canonical unit is the metre. Inch is exact 25.4 mm (CIPM 1959 / NIST).
Result
30.48 cm
in → cm
12 in × 0.0254 = 0.3048 m; 0.3048 ÷ 0.01 = 30.48 cm
- In SI metres0.3048 m
- Factor (from)1 in = 0.0254 m
- Factor (to)1 cm = 0.01 m
- How calculated12 in × 0.0254 = 0.3048 m; 0.3048 ÷ 0.01 = 30.48 cm
- Cross rate1 in = 2.54 cm
Via the metre (SI)
Standards: BIPM SI + international inch (exact 25.4 mm). 12 in × 0.0254 = 0.3048 m; 0.3048 ÷ 0.01 = 30.48 cm
All equivalents
| Unit | Symbol | Value | Factor to metre |
|---|---|---|---|
| mm (millimetre) | mm | 304.8 | 1 mm = 0.001 m |
| cm (centimetre) | cm | 30.48 | 1 cm = 0.01 m |
| dm (decimetre) | dm | 3.048 | 1 dm = 0.1 m |
| m (metre) | m | 0.3048 | 1 m = 1 m |
| km (kilometre) | km | 0.0003048 | 1 km = 1000 m |
| in (inch) | in | 12 | 1 in = 0.0254 m |
| ft (foot) | ft | 1 | 1 ft = 0.3048 m |
| yd (yard) | yd | 0.33333333 | 1 yd = 0.9144 m |
| mi (mile) | mi | 0.000189393939 | 1 mi = 1609.344 m |
| µm (micrometre) | µm | 304,800 | 1 µm = 0.000001 m |
| nmi (nautical mile) | nmi | 0.000164578834 | 1 nmi = 1852 m |
About this tool
Length conversion is a two-step scale change through the metre. Multiply the input by its factor to metres, then divide by the target factor: value_m = value × factor_from; result = value_m ÷ factor_to.
The international inch is defined as exactly 25.4 millimetres (0.0254 m), so 1 foot = 0.3048 m, 1 yard = 0.9144 m, and 1 mile = 1609.344 m. Metric prefixes (µm, mm, cm, dm, km) are exact powers of ten of the metre. The international nautical mile is exactly 1852 m.
Use the all-units table when you need every equivalent at once — sewing, DIY, maps, or school homework. Pair with the percentage calculator for scale factors, or BMI when height is in cm vs inches.
Formula
value_m = value × factor_fromresult = value_m ÷ factor_to1 in = 0.0254 m (exact)1 ft = 0.3048 m · 1 yd = 0.9144 m · 1 mi = 1609.344 m1 cm = 0.01 m · 1 mm = 0.001 m · 1 km = 1000 m
How it is calculated
- Enter a length and pick From / To units.
- Convert to metres: value_m = value × factor_from (e.g. 1 in = 0.0254 m).
- Convert to the target: result = value_m ÷ factor_to.
- Read the step rows for the exact arithmetic of this input.
- Open the equivalents table to see mm, cm, m, in, ft, yd, mi and more at once.
Questions
How does length conversion work?
All lengths go through the metre: multiply by the source factor to get metres, then divide by the target factor. Example: 12 in → 12 × 0.0254 = 0.3048 m → 0.3048 ÷ 0.01 = 30.48 cm.
Is the inch exactly 25.4 mm?
Yes. Since 1959 the international inch is defined as exactly 25.4 millimetres (NIST / BIPM). That makes 1 ft = 0.3048 m and 1 mi = 1609.344 m exact as well.
What about nautical miles?
The international nautical mile is exactly 1852 metres by definition — useful for navigation and aviation.
Are the results official metrology advice?
No. Calculate This is educational. For legal metrology, use your national institute’s guidance and calibrated instruments.