Why is temperature handled differently?

Because Celsius and Fahrenheit do not share a zero point, so converting needs an offset as well as a multiplication. Every other quantity here starts from the same zero, which is why those conversions are a single factor.

Is a kilobyte 1,000 or 1,024 bytes?

Both definitions are in use. SI says 1,000; the older binary convention says 1,024. Storage is sold in the first and often displayed in the second, which is why a one-terabyte drive appears as 931 gigabytes.

How accurate are the conversions?

Exact where the relationship is defined — an inch is precisely 25.4 millimetres by international agreement. Where the factor is a measured constant, enough digits are carried that any rounding is yours to apply.

Why does each quantity have its own unit menus?

Because a single pair of free-text fields could only ever be right for one quantity. An earlier version worked for length and silently produced nonsense for the other nine, which is the kind of bug that only shows up when someone checks the answer.

Unit Converter

Length, mass, area, volume, speed, temperature and data.

Everything runs inside your browser. Your files never leave your device.

Result

The result appears here as you type.

Ask about Unit Converter

Questions about what this tool does, which option to pick, or what it can and cannot handle.

The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong. The tool itself is not guessing: it runs deterministic code on your device.

About the Unit Converter

Converting between units is arithmetic anyone can do and nobody wants to. This handles length, mass, area, volume, speed, temperature, data size, pressure, energy and time, in whichever direction you need.

Each quantity has its own pair of unit menus, generated from the same conversion table the calculation uses. That sounds like an implementation detail and it is the reason the tool works: an earlier version offered ten quantities but only ever accepted units of length, so nine of them silently produced nonsense. A control that changes nothing, or that quietly changes what its neighbours mean, is worse than no control at all, and the arrangement here makes that failure impossible to reintroduce.

Temperature is the one quantity that is genuinely different. Every other conversion here is a multiplication, because the scales share a zero — nought metres is nought feet. Celsius and Fahrenheit do not, so their conversion needs an offset as well as a factor, and it is why 0°C is 32°F rather than 0°F. Kelvin shares its zero with nothing else at all.

Data size carries an ambiguity worth knowing about. A kilobyte is 1,000 bytes by the SI definition and 1,024 by the older binary convention, and both are in use: storage manufacturers sell in the first, operating systems frequently display the second, and the discrepancy is why a one-terabyte drive shows as 931 gigabytes. The unambiguous binary units are kibibyte, mebibyte and gibibyte, which almost nobody says out loud.

Where a conversion is exact it is exact — an inch is defined as precisely 25.4 millimetres — and where it is a measured constant the tool carries enough precision that rounding is yours to do rather than ours.

How to use it

1Pick the quantity you are converting: length, mass, volume, temperature and so on.
2Choose the unit you have and the unit you want from the menus for that quantity.
3Enter the value and read the result.
4For data sizes, check whether you want the decimal or the binary definition — they differ by about seven per cent at gigabyte scale.

Questions

Why is temperature handled differently?: Because Celsius and Fahrenheit do not share a zero point, so converting needs an offset as well as a multiplication. Every other quantity here starts from the same zero, which is why those conversions are a single factor.
Is a kilobyte 1,000 or 1,024 bytes?: Both definitions are in use. SI says 1,000; the older binary convention says 1,024. Storage is sold in the first and often displayed in the second, which is why a one-terabyte drive appears as 931 gigabytes.
How accurate are the conversions?: Exact where the relationship is defined — an inch is precisely 25.4 millimetres by international agreement. Where the factor is a measured constant, enough digits are carried that any rounding is yours to apply.
Why does each quantity have its own unit menus?: Because a single pair of free-text fields could only ever be right for one quantity. An earlier version worked for length and silently produced nonsense for the other nine, which is the kind of bug that only shows up when someone checks the answer.