Length can be expressed in millimetres, centimetres, metres, kilometres or miles, depending on the context. Accurate conversion requires a fixed factor. The metric system is straightforward: one metre contains 100 centimetres and one kilometre contains 1,000 metres. A mile belongs to a different measurement system.
Key conversion formulas
1 m = 100 cm; 1 km = 1,000 m; 1 mile ≈ 1.60934 km. To convert a larger unit into a smaller one, multiply by the relevant factor. To convert in the opposite direction, divide. Round only at the end to avoid unnecessary differences.
Two examples
2.4 kilometres equal 2.4 × 1,000 = 2,400 metres. In the other direction, 850 centimetres equal 850 ÷ 100 = 8.5 metres.
A distance of 5 miles is approximately 5 × 1.60934 = 8.05 kilometres. A rounded figure is often enough for everyday planning, but technical work may require a specified precision. The length converter applies the conversion factor for you.
When do you need a length converter?
Different units appear in sports, travel, DIY projects, technical data sheets and international product specifications. Always check whether a measurement refers to length, height, width or distance.
Common mistakes
- Using 100 instead of 1,000 to convert kilometres to metres.
- Multiplying instead of dividing when converting in the opposite direction.
- Confusing statute miles with nautical miles.
- Rounding too early or omitting the unit symbol.
The International System of Units is explained by Germany’s Physikalisch-Technische Bundesanstalt.
Additional practical tip
When comparing values from different sources, record both the original and converted units. Maps, navigation and aviation may use different types of miles. For precise technical work, document the conversion factor and avoid carrying rounded mental estimates into later calculations.
Read next: Related guide and calculator.
For SI measurement fundamentals, consult the German National Metrology Institute (PTB, German-language PDF).
Convert units in the right direction
A useful rule of thumb is that converting from a larger metric unit to a smaller one makes the number larger. That is why kilometres are multiplied by 1,000 to obtain metres. In the opposite direction, divide by 1,000. Miles and inches use fixed conversion factors because they are not based on the metre’s decimal system. Make sure you do not accidentally use a nautical mile: it is longer than a standard statute mile. For technical drawings, furniture dimensions or sports data, also consider the required precision. Avoid rounding at the first intermediate step if you will use the result in further calculations.
Always keep the unit with the value
A number without a unit is incomplete in a conversion. Include the unit symbol in notes, tables and quotations. This prevents someone from later reading centimetres as metres or miles as kilometres.