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Unit Converter

Convert between units

This converter handles length, weight, volume, and temperature, updating as you type. It covers the metric and imperial units that come up in cooking, travel, DIY, and schoolwork.

Temperature is the one conversion that works differently from the rest. Length and weight scale by simple multiplication, but Celsius and Fahrenheit have different zero points, so converting between them needs an offset as well as a ratio.

How to use it

  1. Pick the category you need: length, weight, volume, or temperature.
  2. Choose the unit you are converting from and the one you want.
  3. Type your value and read the result, which updates as you type.

Conversions worth knowing by heart

  • One inch is exactly 2.54 centimetres, which makes every other length conversion in the imperial system derivable.
  • One kilogram is about 2.2 pounds. For rough mental work, doubling and adding ten per cent is close enough.
  • One mile is about 1.61 kilometres. Multiplying by 1.6 gets you within a per cent for everyday purposes.
  • To convert Celsius to Fahrenheit, multiply by 1.8 and add 32. To go the other way, subtract 32 first, then divide by 1.8.
  • A litre of water weighs a kilogram, which is the quickest bridge between volume and weight in the metric system.

Why unit errors matter

Unit confusion is not a trivial problem. NASA lost the Mars Climate Orbiter in 1999 because one team supplied thrust figures in pound-seconds while the receiving software expected newton-seconds, and the spacecraft entered the atmosphere at the wrong altitude.

The practical lesson for everyday work is to write the unit alongside every number rather than assuming context makes it obvious, particularly in recipes and measurements copied between sources that use different systems.

Frequently asked questions

How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 1.8 and add 32. Going the other way, subtract 32 from the Fahrenheit value first, then divide by 1.8. The offset is needed because the two scales have different zero points.
How many centimetres are in an inch?
Exactly 2.54. This is a defined value rather than an approximation, which is why all other imperial-to-metric length conversions follow from it.
Is a US gallon the same as a UK gallon?
No, and the difference is substantial. A US gallon is about 3.79 litres while an imperial gallon is about 4.55, so recipes and fuel figures do not transfer between them.
What is the quickest way to estimate kilometres from miles?
Multiply by 1.6, or add roughly half again. Sixty miles is about ninety-six kilometres, which is close enough for most practical purposes.