Calculate Conversion publishes free unit converters for length, weight, temperature, volume and speed. There are no accounts and no saved history. Every calculation runs in JavaScript in your browser, so nothing you type is transmitted to us or to anyone else.
Why both scales
A conversion is a relationship between two scales, but almost every converter online reduces it to a single output number and throws the relationship away. That is fine when you want one answer and nothing else. It is unhelpful when you are trying to build an intuition, sanity-check a figure, or read off the value next door.
So each converter here draws both scales as parallel number lines with a shared marker. You see your answer, and you also see that 25 cm is a shade under 10 in, that the Celsius and Fahrenheit scales run at different rates, that a US and an imperial gallon are visibly not the same length of line.
Where the conversion factors come from
Most imperial and US customary units are defined exactly in metric terms by the international yard and pound agreement of 1959, and by subsequent national legislation. Where a factor is exact, this site treats it as exact.
| Unit | Exact definition |
|---|---|
| Inch | 25.4 mm |
| Pound | 0.45359237 kg |
| US gallon | 3.785411784 L |
| Imperial gallon | 4.54609 L |
| Nautical mile | 1852 m |
Reference definitions follow those maintained by the International Bureau of Weights and Measures (BIPM) and the US National Institute of Standards and Technology (NIST).
Two expanded examples show how this policy works in practice: the printable kitchen conversion chart keeps US, metric and imperial measures visibly separate, while 180 cm in feet and inches preserves the exact factor and explains each rounding choice.
Where units are genuinely ambiguous
Some unit names mean different amounts in different places, and no amount of precision fixes that. A ton can be three different masses. A gallon can be two different volumes. A cup can be four. Rather than quietly picking one and hoping, every affected converter lists each variant separately and the article explains the difference.
Accuracy and its limits
Results are computed in double-precision floating point and displayed to a sensible number of significant figures, which is ample for cooking, travel, DIY and study.
For legal, medical, structural or trade-measurement work, verify against the governing standard for your jurisdiction. A web converter is a convenience, not a certified instrument, and this one carries no warranty.
Corrections
If a factor is wrong or a page is unclear, please write to hello@calculateconversion.online. Corrections are made on the page itself.
How the site is funded
Calculate Conversion is free and funded by advertising. Ads are labelled, kept below or beside the content, and never placed against the converter controls where they could be clicked by accident. No advertiser has any involvement in what these pages say.
Last updated 13 September 2026.