A Quick Reference Guide to Metric and Imperial Conversions

Most of the world uses the metric system, while a handful of countries, including the United States, primarily use imperial units. That split shows up constantly — in recipes, travel, DIY projects and fitness tracking — and getting a conversion wrong can be more than a minor inconvenience.

Length

One inch equals 2.54 centimetres, one foot equals 0.3048 metres, and one mile equals 1.60934 kilometres. These factors stay constant regardless of the size of the number you're converting.

Weight

One pound equals roughly 0.4536 kilograms, and one kilogram equals about 2.2 pounds. For quick mental estimates, doubling a kilogram figure and subtracting 10% gets you close to pounds.

Temperature

Unlike length and weight, temperature conversions aren't a simple multiplication — they involve an offset. Celsius to Fahrenheit is calculated by multiplying by 9/5 and adding 32, while Fahrenheit to Celsius subtracts 32 first, then multiplies by 5/9.

Why precision matters

In cooking, a few degrees can be the difference between properly set custard and a curdled mess. In construction or engineering, a rounding error compounded across many measurements can create a real structural problem. It's worth using an exact calculation rather than a rough mental estimate for anything that matters.

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Our Length Converter, Weight Converter and Temperature Converter handle the exact maths for you.