Unit converter — offline

Unit conversion is arithmetic, and it should not require a page full of adverts or a network request. Pick a category, choose the units, type a value, and the result appears — computed in your browser, working offline once the page has loaded, which is exactly when you tend to need it: in a kitchen, on a plane, in a workshop, or abroad on a bad connection.

Length, weight, area, volume, speed, temperature, and data sizes are all covered.

Conversions use the standard definitions rather than rounded approximations — one inch is exactly 25.4 millimetres, and the rest follow from the same official factors. Results are presented without the floating-point artefacts that make so many online converters report things like 2.0000000000000004, which is unsettling even when it is technically almost right.

Temperature is the category worth pausing on, because it is the one that behaves differently. Every other conversion here is a simple multiplication, but temperature scales have different zero points, so Celsius to Fahrenheit needs an offset as well as a factor. That is why you cannot convert a temperature difference the same way you convert a temperature: a rise of 10 °C is a rise of 18 °F, not 50 °F.

Data sizes are offered in both 1000-based and 1024-based forms, because the world genuinely disagrees about what a kilobyte is and the gap is not small.

Under the SI convention a kilobyte is 1,000 bytes, and this is what storage manufacturers use — which is why a "1 TB" drive shows up as about 931 GB in Windows. The binary convention, properly written KiB, MiB, and GiB, uses 1,024 and is what operating systems and memory sizes actually use. The two diverge by roughly 2.4% at the kilobyte level and about 10% by the terabyte, so the distinction matters for capacity planning and bandwidth calculations even though it is usually invisible day to day.

Related and equally local: percentage calculator and number base converter.