Volume is where the two measuring systems disagree most, and where they disagree quietly. A US gallon is 3.785 litres and an imperial gallon is 4.546 — a fifth larger — so the same car appears to do noticeably better on British fuel figures. The fluid ounce reverses the trick: the imperial one is the smaller of the two, because the larger imperial gallon splits into 160 parts rather than 128. Every converter here says which system it means, and the pages spell out the trap rather than leaving it to be discovered.
Tools in this category
Imperial Gallons to Liters
Convert UK gallons to litres. The imperial gallon is 4.54609 litres exactly, a fifth larger than the US gallon it is often confused with.
Fluid Ounces to Milliliters
Convert US fluid ounces to milliliters in your browser, with the difference from the UK ounce spelled out.
Quarts to Liters
Convert US quarts to liters in your browser. A quart is 0.946 liters, which is why it gets mistaken for one.
Cups to Milliliters
Convert US cups to milliliters in your browser, and find out why a cup of flour is not a reliable measurement.
Gallons to Liters
Convert US gallons to liters in your browser, with a warning about the UK gallon, which is a fifth larger.
Liters to Gallons
Convert liters to US or imperial gallons. The two gallons differ by about twenty percent, so this converter keeps them as separate units rather than guessing.
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How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.