Volume Converter

One US gallon is 3.785 L, and one cup is anywhere from 200 to 250 mL

Every volume unit on this page hangs off the liter. One liter is the volume of a cube 10 cm on a side (1 dm³), so it equals 1,000 mL and 1,000 cm³; a cubic meter (m³) holds 1,000 L. A US gallon is defined as 231 cubic inches, which makes it exactly 3.785411784 L. The imperial gallon used in UK recipes and older British figures is 4.54609 L, about 20% larger.

The names that cause the most trouble are the ones that look the same. A US customary cup is 236.59 mL (8 US fluid ounces), the cup on a US Nutrition Facts label is 240 mL, a metric cup as used by Health Canada and Australia's Eat for Health is 250 mL, and a Japanese measuring cup is 200 mL. The converter above lines these up in the cards below the result, so when a recipe does not say which cup it means you can see how far apart the answers are.

When you need to convert volume

• Cooking from a recipe written for another country: a US recipe asks for 2 cups, a British one for half an imperial pint, an Australian one for 250 mL. For 2 cups the gap between the US customary cup (473.2 mL) and the metric cup (500 mL) is about 27 mL, enough to matter in baking.
• Reading a label or a product page: an American product may give its size in gallons or fl oz, and a Nutrition Facts panel uses fl oz and mL side by side. Converting to liters or mL lets you compare it with a product sized in metric units.
• Filling an aquarium, tank or pool: you measure width, depth and height, and need liters or gallons for dosing a conditioner or sizing a pump. The "By width, depth, height" mode does this directly in inches, feet, centimeters or meters.
• Estimating bulk material: soil, mulch or gravel quoted in cubic yards, cubic feet or cubic meters all convert to one another here. A cubic yard is 27 ft³, or 764.55 L.
• Comparing a US and a UK figure: a "gallon" or a "pint" quoted from a British source is not the same quantity as one quoted from an American source.

How to use the converter

1. Type a number in "Value" and choose its unit under "Unit". Fractions such as 1/2 or 1 1/2 are accepted. The line under the unit shows how many mL or L one of that unit is.
2. Pick "Convert to" and the result appears in large type. The swap button (⇄) exchanges the two units.
3. Under the result, "Reverse" gives one target unit in the unit you entered, "If it were water (20 °C)" gives the weight of that much water, and "As a cube" gives the edge of a cube of the same volume.
4. The measuring jug has two scales: the left one is the unit you entered, the right one the unit you are converting to. Drag the water level or tap the jug and the value is filled in; focus the handle and use the arrow keys to move one small mark at a time.
5. If you only know the size, press "By width, depth, height", choose box or cylinder, pick mm, cm, m, in or ft, and enter the sizes (diameter and height for a cylinder).
6. Tap any card under "See every unit" to make it the target. Choose 4, 6 or 10 significant figures, and use "Copy result" or "Copy link" to carry the value or the current setup elsewhere.

How the calculation works

The converter multiplies your value by the size of the unit you entered, in liters, then divides by the size of the unit you want. Two US customary cups in mL is 2 × 236.5882365 = 473.176473 mL; 500 mL in US customary cups is 500 ÷ 236.5882365 ≈ 2.11 cups. Every unit size is fixed by definition, so no rounding enters until the result is shown.

• Metric: 1 L = 1 dm³ = 1,000 cm³ = 0.001 m³.
• US units: since 1959 an inch has been exactly 25.4 mm (NIST), so a cubic inch is 16.387064 cm³. The US gallon is 231 in³, which gives 231 × 16.387064 = 3,785.411784 cm³ = 3.785411784 L. It is also 128 fluid ounces, and NIST defines the cup, tablespoon and teaspoon as 8, ½ and ⅙ fluid ounce.
• UK units: the Weights and Measures Act 1985, Schedule 1, sets the gallon at 4.54609 dm³ and the pint at 0.56826125 dm³, with the fluid ounce as 1/20 of a pint.

The metric ladder

Liter-family units step by 10; cubic-meter-family units step by 1,000, because a cubic unit multiplies a length three times and a tenfold length is a thousandfold volume. The two families meet at 1 dm³ = 1 L and 1 cm³ = 1 mL.

How big one unit is

The middle column is the exact value that follows from the definition; the right column rounds it to 4 significant figures. Where a value is marked with ≈ in the middle column it is itself rounded.

Cups and spoons depend on the standard

A cup is not a unit in the metric system, so how many mL a recipe means by "1 cup" depends on the standard behind it. Even within the United States there are two: the customary cup of 8 fluid ounces (236.59 mL), and the 240 mL cup that the FDA's labeling rule uses on Nutrition Facts panels. Canada's food guide gives 250 mL = 1 cup, and Australia's Eat for Health writes "1 cup (250ml)". If a recipe states its own measuring standard, follow that one.

Spoons differ by much less. A metric tablespoon is 15 mL and a metric teaspoon 5 mL (the same figures the FDA uses on labels); a US tablespoon (½ fl oz) is 14.79 mL and a US teaspoon (⅙ fl oz) is 4.93 mL. NIST itself notes that 15 mL and 5 mL are rounded values for the US spoons, so for a single spoonful the two are interchangeable in a home kitchen. They do add up: a US customary cup is 16 US tablespoons, but 16 metric tablespoons is 240 mL, so filling a cup by spoon gives a different amount depending on the standard.

US and imperial gallons, quarts, pints, ounces

The US and the UK use the same names for different amounts. The imperial gallon, quart and pint are each about 20% larger than the US ones. The fluid ounce goes the other way: an imperial fluid ounce (28.41 mL) is about 4% smaller than a US one (29.57 mL), because an imperial pint is divided into 20 fluid ounces and a US pint into 16. So a UK pint of 20 imperial fl oz is 568.26 mL, which is 95.08 mL more than a US pint of 16 US fl oz at 473.18 mL.

A "gallon" in an American source is a US gallon and in a British source an imperial gallon. If the origin is unclear, put both gallons side by side in the converter and remember that the two answers are about 20% apart.

Working out liters from width, depth and height

A box holds width × depth × height, and a cylinder holds π × (diameter ÷ 2)² × height. Measured in cm the product is in cm³, and dividing by 1,000 gives liters; measured in meters it is in m³, and multiplying by 1,000 gives liters. In inches, divide cubic inches by 231 for US gallons. All three sizes must be in the same length unit.

These figures use the dimensions exactly as measured. A glass aquarium is smaller inside by the thickness of the glass and is rarely filled to the brim, so the water it really holds is less than the table shows. If a dose depends on the amount of water, use the inside dimensions and the actual water depth.

From volume to weight

Volume is not weight: 1 L of water, milk and oil weigh different amounts. To get a weight you multiply by the density of that substance. Water is heaviest near 4 °C, where 1 L is about 1 kg, and at 20 °C one mL is 0.998207 g, so a liter is about 998.2 g. The "If it were water" line uses that 20 °C value.

A cubic meter of water weighs close to 1,000 kg (about 998.2 kg at 20 °C). The table does not apply to syrup, oil or any liquid other than water.

Common mistakes

• Mixing up US and imperial gallons: 5 imperial gallons is 22.73 L, but calculating it as US gallons gives 18.93 L, about 17% too little.
• Treating a fluid ounce as an ounce of weight: a fluid ounce (fl oz) measures volume and an ounce (oz) measures weight. An avoirdupois ounce is about 28.35 g, and US nutrition labeling uses 28 g. A US fluid ounce of water weighs close to 29.5 g, which looks similar, but for flour or oil the difference is large.
• Dividing cm³ by 100 to get liters: 1 L is 1,000 cm³, so divide by 1,000.
• Confusing cubic feet with square feet: ft³ is volume, ft² is area. Covering 100 ft² with 2 inches of mulch needs 100 × (2 ÷ 12) ≈ 16.7 ft³, which is about 0.62 yd³.
• Mixing length units in one calculation: entering width and depth in cm and height in m and multiplying them leaves the answer 100 times off. Put all three in one unit first.
• Assuming "a cup" is one amount: see the cups table above, where the four standards span 200 to 250 mL.

Limits and cautions

• This is a calculator that applies defined conversion factors. It does not model how a liquid's volume changes with temperature.
• The "If it were water" weight assumes pure water at 20 °C. It does not suit seawater, milk, oil or anything else.
• Cylinder volumes use π, so they are always shown as rounded (≈). A bucket with a tapered or rounded body will differ from the cylinder formula.
• Kitchen measuring cups and spoons carry their own marking error. For trade, medicine or lab work that needs a known amount, use calibrated equipment.
• The converter cannot tell which "cup" or "gallon" your source meant. Check the recipe's or label's own standard first.

Basis: US units from NIST, UK units from the Weights and Measures Act 1985, US nutrition-label units from 21 CFR 101.9, and the density of water from NIST. All checked on 20 October 2026.

Sources

• 01NIST SP 1038 - The International System of Units (SI): Conversion Factors for General UseUS gallon = 128 fl oz (231 in³); cup, tablespoon, teaspoon = 8, ½, ⅙ fl oz (footnote 19)
• 02NIST Handbook 44 (2024) - Appendix C: General Tables of Units of Measurement1 cup = 8 fluid ounces (exact); 15 mL and 5 mL for tablespoon and teaspoon are rounded values
• 03NIST SP 811 Appendix B.8 - Factors for units listed alphabeticallyImperial gallon 4.546 09 L (exact); ounce (avoirdupois) 28.349 52 g
• 04NIST - SI Units: Length1 in = 25.4 mm from 1 July 1959
• 05legislation.gov.uk - Weights and Measures Act 1985, Schedule 1gallon 4.546 09 dm³, pint 0.568 261 25 dm³, fluid ounce 1/20 pint
• 06eCFR - 21 CFR 101.9 Nutrition labeling of food(b)(5)(viii) teaspoon 5 mL, tablespoon 15 mL, cup 240 mL, 1 fl oz 30 mL, 1 oz 28 g
• 07Health Canada - Canada's food guide, measuring ingredients250 mL = 1 cup
• 08Australian Government - Eat for Health, Serve sizes1 cup (250ml)
• 09Osaka City - cups and spoons and food weight (Japanese)1 cup = 200 ml, 1 tablespoon = 15 ml, 1 teaspoon = 5 ml
• 10NIST Chemistry WebBook - Thermophysical Properties of WaterDensity 0.998207 g/mL at 20 °C and 0.101325 MPa

Frequently asked questions

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