Same name, two gallons
Volume conversion goes wrong in the gap between two units that share a name.
The US liquid gallon is 231 cubic inches. The inch is fixed at 25.4 mm, so the gallon comes out to exactly 3.785411784 litres. The imperial gallon, still the one on UK fuel pumps and behind the bar, is exactly 4.54609 litres. Divide the two. The imperial gallon holds 1.20095 US gallons.
A 20 litre jerrycan is 5.28 US gallons. The same container is 4.40 imperial gallons. Fill a boat tank from the wrong column and you are short by about a fifth.
Twenty percent.
The dropdown uses the spelling Liter. Litre and liter are one unit.
| Name | US liquid | Imperial | What the gap means |
|---|---|---|---|
| Gallon | 3.785411784 L | 4.54609 L | Imperial is 20.1% larger |
| Quart | 0.946353 L | 1.136523 L | Each is a quarter of its own gallon |
| Pint | 473.176 mL | 568.261 mL | The pub pint is the imperial one |
| Fluid ounce | 29.5735 mL | 28.4131 mL | Imperial ounce is the smaller one |
| Cup on this page | 236.588 mL | 284.131 mL | The 250 mL metric cup is a separate measure |
The fluid ounce row is the one people skip. A US gallon is split into 128 fluid ounces. An imperial gallon is split into 160. The larger gallon is cut into more pieces, so each piece shrinks. Eight US fluid ounces are a customary cup, 236.6 mL. Eight imperial fluid ounces are 227.3 mL.
A recipe line that reads "8 fl oz of cream" follows the country of the book. No country on the line, no reliable pour.
Pour the cup before you scale
Cup (US) here is the customary cup, 8 US fluid ounces, 236.588 mL. US nutrition labels print a 240 mL cup. Cookbooks from Australia, New Zealand, and Canada usually mean a 250 mL metric cup. A Japanese cup is 200 mL. Four cups, one English word.
Cup (UK) is half an imperial pint: 10 imperial fluid ounces, 284.131 mL.
A Melbourne book that says "1 cup of milk" almost always means 250 mL. Choose Cup (US) and the readout returns 236.6 mL. One cake still bakes. Four cups of the same miss is 53.6 mL. A brine carries the miss into the salt.
1 cup of milk, read before you multiply the recipe
Recipe open, jug marked in millilitres? Put the cup count in the field above before you multiply anything. Set From to Cup (US) or Cup (UK). Set To to Milliliter. Pour to the figure. Then scale. Scaling a mismatched cup multiplies the miss.
Spoons without a country
Tablespoon and Teaspoon on this form are the US sizes. One tablespoon is 14.7868 mL. One teaspoon is 4.9289 mL. Three teaspoons make that tablespoon.
Australia's tablespoon is 20 mL. A metric tablespoon, common across Europe, is 15 mL, with a 5 mL teaspoon beside it. The gap against the US teaspoon is 0.07 mL, which baking soda forgives. Leave a medicine dose on the device that came with the bottle. Dosing marks are 5 mL and 15 mL. A syrup does not need a customary-unit surprise.
The option labels should name the country. They do not. Treat both spoons as US, or work the 15 mL and 20 mL step on paper.
A litre became a cube in 1964
From 1901 until 1964, the litre was the space taken by 1 kg of pure water at its densest. That volume measured 1.000028 cubic decimetres. In 1964 the General Conference on Weights and Measures set 1 litre equal to 1 cubic decimetre. From then on, 1 mL and 1 cm³ are the same space. The Milliliter row and the Cubic Centimeter row should agree. A difference is rounding in the script, not a second unit hiding in the list. Glassware marked against the old water litre sits about 28 parts per million off a modern flask. A kitchen ignores the gap. A calibration note should say which litre it was written against.
A cubic metre is 1,000 litres. A cubic foot is 28.316846592 litres. A cubic yard is 27 cubic feet, 764.555 litres. "A yard of concrete" means that cube. A supplier quoting a length has not quoted a volume.
Three edge lengths and no volume yet? Work the solid on the volume calculator, then bring the cubic result here. The edge lengths themselves belong on the length converter. A floor or a slab face belongs on the area converter. This page starts once the quantity is already a volume.
Bring a volume, not a weight
Flour, sugar, and rice show up in grams. A cup of flour packs nothing like a cup of water. Ingredient factors for that kitchen case live on the grams to cups page linked above. Density is the general version, mass per space, on the density converter. Neither job is a unit swap.
Fuel economy is a gallon trap with a different shape. Thirty miles per US gallon is about 36 miles per imperial gallon, because the imperial gallon is the larger bucket. The fuel converter is built for that switch. Divide a distance by a gallon you already converted here and the same correction lands twice.
This page will not save you from these
- Dry pint
- US produce and grain quotes often mean the dry pint, about 550.6 mL, against a liquid pint of 473.2 mL. The select list has liquid pints only. Confirm the quote before you convert.
- Rounded factors
- The legal figures in the table keep the defined digits. The script stores about six figures of each factor. A kitchen and a job site will live with the trim. A fuel custody transfer should use the factor written in the contract.
- Repeat trips through the script
- Each pass uses JavaScript numbers. Run one value back and forth many times and the last digit wanders. For a figure someone else will audit, quote the source value and the factor.
- Links you forward
- Copy link writes the value and both units into the URL. The maths stays on your machine. The link does not. Leave a confidential tank volume out of any URL you send on.