Metric and imperial units rarely meet at a clean round number, and that is where converting by hand tends to go wrong. This handles length, weight, temperature, area, volume, speed, data and time, with both sides updating live as you type into either one.
When you'd use this
Anywhere a spec, a recipe, or a measurement arrives in a unit your audience (or your code) doesn't use natively: a US recipe's cups and ounces going metric, or a data sheet's millimetres going to inches.
Common errors
Temperature is the one category here that doesn't reduce to simple multiplication. Celsius, Fahrenheit and Kelvin each start from a different zero point, so scaling by a ratio the way you would for length or weight produces a wrong answer. This tool applies the correct formula for each pair automatically.
Frequently asked questions
Why don't metric-to-imperial conversions come out as round numbers?
The two systems aren't tied together by a clean ratio. A metre is defined independently of a foot, so almost every cross-system conversion lands on a repeating or long decimal. That's a property of the units themselves, not a rounding fault in the conversion.
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