Volume Converter
Litres, millilitres, cubic feet, and every US and imperial gallon, pint, cup and fluid ounce — each one labelled US or Imperial, because they are different sizes and the difference runs the wrong way half the time.
Convert a volume
The measurement you have, in the unit chosen below.
The unit the measurement is already in. US and imperial units are listed separately because they are different sizes.
The unit you want the answer in. Every other unit is listed underneath the result anyway.
Everything routes through the litre: 1 US gal is 3.785411784 L, and one L is exactly 1 L.
- Conversion factor
- 1 US gal = 3.785411784 L
- Reverse factor
- 1 L = 0.2641720524 US gal
- In litres
- 3.785411784 L
- Both gallons
- 1 US gal = 0.8326741846 imp gal
- Both fluid ounces
- 128 US fl oz = 133.2278695 imp fl oz
- Definition
- One litre is exactly one cubic decimetre — a cube 10 cm on each side.
| Unit | Symbol | Value |
|---|---|---|
| Millilitres | mL | 3,785.411784 |
| Cubic centimetres | cm³ | 3,785.411784 |
| Litres | L | 3.785411784 |
| Cubic metres | m³ | 0.003785411784 |
| Cubic inches | in³ | 231 |
| Cubic feet | ft³ | 0.1336805556 |
| US teaspoons | US tsp | 768 |
| US tablespoons | US tbsp | 256 |
| US fluid ounces | US fl oz | 128 |
| US cups | US cup | 16 |
| US pints | US pt | 8 |
| US quarts | US qt | 4 |
| US gallons | US gal | 1 |
| Imperial fluid ounces | imp fl oz | 133.2278695 |
| Imperial pints | imp pt | 6.661393477 |
| Imperial gallons | imp gal | 0.8326741846 |
Every conversion goes through the litre
Sixteen units could be connected by 256 direct factors, and a table that size cannot be kept consistent. Instead each unit is stored as one number — how many litres it is — and every conversion is two steps.
litres = value × f(from) • result = litres ÷ f(to)- f(u)
- Litres in one unit u — 3.785411784 for the US gallon
- litres
- The measurement in the metric base unit
- result
- The measurement in the unit you asked for
What makes this exact rather than approximate is where the factors come from. These are definitions, not measurements:
- 1 US gallon = 231 cubic inches exactly. The inch has been exactly 0.0254 m since 1959, so a cubic inch is exactly 16.387064 mL and the US gallon is exactly 3.785411784 litres. Every smaller US liquid unit is a plain fraction of it: quart a quarter, pint an eighth, cup a sixteenth, fluid ounce a 128th, tablespoon a 256th, teaspoon a 768th.
- 1 imperial gallon = 4.54609 litres exactly — the value Canada fixed in 1976 and the United Kingdom wrote into the Weights and Measures Act 1985. It is cut into 8 pints of 20 fluid ounces each, so 160 fluid ounces to the gallon.
- 1 litre = 1 cubic decimetre exactly. Declared by the 12th CGPM in 1964, which is what makes a millilitre and a cubic centimetre the same volume with nothing between them.
- 1 cubic foot = 1,728 cubic inches, or 28.316846592 litres — the 7.48 US gallons per cubic foot that pool, tank and aquarium sizing runs on.
The two systems disagree in both directions
This is the one thing worth taking away from the page. The US gallon is smaller than the imperial gallon: 3.785411784 L against 4.54609 L, about 17% less. But the US fluid ounce is larger than the imperial fluid ounce: 29.5735295625 mL against 28.4130625 mL, about 4% more.
Both facts come from the same place. The US gallon holds 128 fluid ounces; the imperial gallon holds 160. A bigger container cut into more pieces gives smaller pieces. So the sign of a transcription error flips halfway down the ladder — quantities written in gallons, quarts or pints come out short when read as US, and quantities written in fluid ounces come out long. That is why every ambiguous unit on this page carries its system in the name, and why the result panel always shows your volume in both gallons and both fluid ounces at once.
Results are rounded to twelve significant figures rather than to a fixed number of decimal places. This tool spans the millilitre to the cubic metre, a factor of a million, and no single decimal place is readable at both ends. Significant figures are also what makes one US gallon come back as exactly 231 cubic inches: 3.785411784 ÷ 0.016387064 in binary floating point is 230.99999999999997.
One US gallon, all the way down
Start from the definition. One US gallon is 231 cubic inches. One cubic inch is 0.0254³ cubic metres, which is exactly 16.387064 millilitres. So 231 × 16.387064 = 3,785.411784 mL, or 3.785411784 litres. Nothing is rounded anywhere in that line — it is two definitions multiplied together.
Now the same gallon in imperial terms. 3.785411784 ÷ 4.54609 = 0.8326741846 imperial gallons. Filling a US gallon jug from an imperial gallon leaves 0.760678216 litres behind — three quarters of a litre, or about one and a third imperial pints.
Where that bites: fuel economy. A car advertised at 45 mpg in Britain is being measured per imperial gallon. Convert the gallon, not the miles: 45 × 0.8326741846 = 37.5 miles per US gallon. The car is identical; the number drops by a sixth because the gallon did.
And in a kitchen.A British recipe calling for one pint of stock wants 568.26125 mL. Measured with a US pint jug you get 473.176473 mL — 95 mL short, two fifths of a US cup missing. But the same recipe written as “8 fl oz of cream” works the other way: 8 imperial fluid ounces is 227.3045 mL, while 8 US fluid ounces is 236.5882365 mL, so the American cook adds slightly too much. Same recipe, same page, opposite errors.
What this converter assumes
- All US units here are liquid measure. The US dry gallon, dry quart and dry pint belong to a separate system used for produce sold by volume and are about 16% larger; they are deliberately not offered.
- The US cup is the customary 236.5882365 mL cup that recipes mean, not the 240 mL “legal” cup defined for FDA nutrition labelling.
- Only US teaspoons and tablespoons are offered. A metric tablespoon is 15 mL and an Australian one is 20 mL, and a fourth spoon labelled only “tablespoon” would cause more errors than it solves.
- A volume is a magnitude, so negative values are rejected. If you are converting a difference between two measurements, convert its size and keep the sign yourself.
- Results carry twelve significant figures internally and are displayed to ten. Neither is a claim about your measurement — a jug read to the nearest 10 mL is still only good to 10 mL after conversion.
- Nothing here converts volume to weight. A litre of water is about a kilogram, a litre of honey is about 1.4 kg, and a litre of flour is about 0.53 kg. That conversion needs a density and is a different calculation.
Volume conversion FAQ
How many litres are in a gallon?
That question has two answers, which is the whole problem. A US gallon is exactly 3.785411784 litres. An imperial gallon is exactly 4.54609 litres — about 20% larger. There is no such thing as an unqualified gallon, so this converter never offers one: every gallon, quart, pint and fluid ounce in the lists is labelled US or Imperial before you can pick it.
Why is a US fluid ounce larger than an imperial one when the US gallon is smaller?
Because the two systems cut their gallons into a different number of ounces. The US gallon is 128 fluid ounces; the imperial gallon is 160. A larger gallon divided into more parts gives a smaller part, so the imperial fluid ounce comes out at 28.4130625 mL against the US 29.5735295625 mL — the US one is about 4% bigger. This is why the direction of a transcription error flips depending on which unit the recipe used: gallons and pints come out short, fluid ounces come out long.
How much bigger is a UK pint than a US pint?
An imperial pint is 20 imperial fluid ounces, 568.26125 mL. A US liquid pint is 16 US fluid ounces, 473.176473 mL. The imperial pint is 20.095% larger, or put the other way, a US pint is 16.7% smaller — 95 mL short on every pint. That is roughly two fifths of a US cup missing from a pint of stock.
Is a millilitre exactly the same as a cubic centimetre?
Today, yes, exactly. The 12th General Conference on Weights and Measures declared in 1964 that 'litre' is a special name for the cubic decimetre, which makes 1 mL and 1 cm³ the same volume by definition. Between 1901 and 1964 they were not: the litre was then the volume of one kilogram of pure water at maximum density, which turned out to be 1.000028 dm³. Old, very precise chemistry results quoted in litres are 28 parts per million larger than the same number of cubic decimetres.
How do I convert UK miles per gallon to US miles per gallon?
Multiply by 0.8327 — or equivalently divide by 1.20095 — because a US gallon is 0.8326741846 imperial gallons. A car advertised at 45 mpg in Britain returns 37.5 mpg on the same fuel in America. Nothing about the car changed; the gallon did. Going the other way, multiply the US figure by 1.20095.
Which cup does a US recipe mean, 236.6 mL or 240 mL?
Recipes mean the US customary cup, which is exactly 8 US fluid ounces, or 236.5882365 mL — and that is the cup this converter uses. The 240 mL 'legal' cup is a rounded value defined for FDA nutrition labelling, so it is what a serving size on a packet refers to. The two are 1.4% apart, which never matters in a kitchen and does matter if you are reconciling a label against a formulation.
Is a tablespoon 15 mL?
Not quite, and it depends where you are. A US tablespoon is exactly 3 US teaspoons, 14.78676478125 mL. The metric tablespoon used across most of Europe is a round 15 mL. An Australian tablespoon is 20 mL — four teaspoons, not three — which is a 35% error against a US recipe and enough to ruin anything leavened. This converter offers the US spoons only, for exactly that reason: a spoon labelled just 'tablespoon' would be a trap.
What is a US dry pint, and why is it not in the list?
It is a unit from a separate system used for produce sold by volume — berries, grain, shellfish. A US dry pint is 0.5506104713575 litres, about 16% larger than the 473.176473 mL liquid pint. Offering both with only the word 'dry' between them would create a new confusion to replace the one this tool is trying to remove, so only the liquid units are here.
Sources and review notes
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), including the exact conversion factors used here
- NIST Handbook 44 — Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, for the US customary capacity units
- BIPM — The International System of Units (SI) Brochure, for the 1964 declaration that the litre is the cubic decimetre
- Weights and Measures Act 1985 (UK) — the imperial gallon as exactly 4.54609 cubic decimetres
The factors on this page are defined values rather than measured ones, so they do not go stale: the US gallon has been exactly 231 cubic inches for centuries and exactly 3.785411784 litres since the inch was fixed in 1959, and the imperial gallon has been exactly 4.54609 litres since the 1970s and 1980s. What changes is only which system a given document meant.