Length Converter

How it is calculated

The tool converts through metres. First the input is multiplied by the number of metres in the chosen unit: metres = value × factor. Then each of the eight output units is found with result = metres ÷ factorunit. The factors are exact definitions: 1 km = 1000 m, 1 cm = 0.01 m, 1 mm = 0.001 m, 1 mi = 1609.344 m, 1 yd = 0.9144 m, 1 ft = 0.3048 m and 1 in = 0.0254 m. Every result is rounded to two decimals, so a very small length in a large unit can show as 0.00. An unrecognised unit is treated as metres, and negative values are converted as they are.

Common mistakes

• Mixing up miles (mi) and metres (m) in the unit selector. The same number differs by a factor of about 1,609.
• Reading the rounded result as exact. Only two decimals are shown, so 5 m appears as 0.00 mi and cannot be used for fine work in large units.
• Confusing millimetres (mm) with centimetres (cm), which are a factor of ten apart.
• Entering a nautical mile or a survey foot, which are not among the eight units. They are different lengths from the international mile and foot used here.
• Typing the value with a decimal comma (1,5) or thousands separators (1,234.5). These are not read as numbers and no result appears; write 1.5 instead.