How Unit Conversion Works: A Simple Guide

What is unit conversion?

Unit conversion changes a measurement from one unit into another without changing the quantity itself. One metre and 100 centimetres describe the same length.

The key is knowing the relationship, or conversion factor, between the two units.

Want to try the idea yourself? Use the Unit Converter.

Using a conversion factor

If 1 inch equals 2.54 centimetres, convert 10 inches by multiplying 10 by 2.54. The result is 25.4 cm.

To go the other way, divide centimetres by 2.54. Keeping track of which unit you start with helps avoid reversing the calculation.

Metric conversions

Metric units are often straightforward because prefixes represent powers of ten. One kilometre is 1,000 metres, one metre is 100 centimetres and one kilogram is 1,000 grams.

Moving between these units is therefore usually multiplication or division by 10, 100 or 1,000.

Temperature is different

Temperature conversions are not simple scale multiplications because Celsius and Fahrenheit have different zero points. Fahrenheit to Celsius uses (F - 32) × 5/9, while Celsius to Fahrenheit uses C × 9/5 + 32.

That is why applying the same conversion method used for length or weight gives the wrong answer.

Convert without memorising formulas

The Unit Converter handles common conversion factors automatically, making it useful when switching between metric and imperial measurements.

Always include the unit with your result. A number without its unit can be ambiguous or misleading.