CalcOpenly

Volume converter

Convert gallons to litres, cups to mL and fl oz to mL exactly, with US and imperial gallons, pints and fluid ounces kept separate.

Updated Checked against 5 worked examples

A number in the “from” unit, or with its own unit
Try
Converted value
L
Converted value: 3.785411784 L
Shown to 12 significant figures, half-up
Conversion
1 gal = 3.785411784 L
Conversion factor
3.785411784
Exactness
Exact

1 gal is exactly 3.785411784 L.

The same amount counted in each unit

gal1 galL3.785411784 L
1 gal in every volume unit (24 rows)
UnitValueDefinition
cubic metre (m³)0.003785411784Base unit
litre (L)3.7854117841 L = 0.001 m³, exact
millilitre (mL)3,785.4117841 mL = 0.000001 m³, exact
centilitre (cL)378.54117841 cL = 0.00001 m³, exact
decilitre (dL)37.854117841 dL = 0.0001 m³, exact
cubic inch (in³)2311 in³ = 0.000016387064 m³, exact
cubic foot (ft³)0.13368061 ft³ = 0.028316846592 m³, exact
cubic yard (yd³)0.0049511321 yd³ = 0.764554857984 m³, exact
US gallon (gal)11 gal = 0.003785411784 m³, exact
US quart (qt)41 qt = 0.000946352946 m³, exact
US pint (pt)81 pt = 0.000473176473 m³, exact
US cup (cup)161 cup = 0.0002365882365 m³, exact
US fluid ounce (fl oz)1281 fl oz = 0.0000295735295625 m³, exact
US tablespoon (tbsp)2561 tbsp = 0.00001478676478125 m³, exact
US teaspoon (tsp)7681 tsp = 0.00000492892159375 m³, exact
imperial gallon (gal (UK))0.83267421 gal (UK) = 0.00454609 m³, exact
imperial quart (qt (UK))3.3306971 qt (UK) = 0.0011365225 m³, exact
imperial pint (pt (UK))6.6613931 pt (UK) = 0.00056826125 m³, exact
imperial fluid ounce (fl oz (UK))133.22791 fl oz (UK) = 0.0000284130625 m³, exact
metric cup (cup (metric))15.141651 cup (metric) = 0.00025 m³, exact
metric tablespoon (tbsp (metric))252.36078561 tbsp (metric) = 0.000015 m³, exact
metric teaspoon (tsp (metric))757.08235681 tsp (metric) = 0.000005 m³, exact
oil barrel (bbl)0.023809521 bbl = 0.158987294928 m³, exact
acre-foot (ac·ft)0.0000030688831 ac·ft = 1,233.48183754752 m³, exact
How it's calculated S

  1. Convert US gallon to cubic metre

    1 gal×0.003785411784 m3gal=0.003785411784 m31\ \text{gal} \times 0.003785411784\ \tfrac{\text{m$^{3}$}}{\text{gal}} = 0.003785411784\ \text{m$^{3}$}

    1 gal = 0.003785411784 m³, exact

  2. Convert cubic metre to litre

    0.003785411784 m3÷0.001 m3L=3.785411784 L0.003785411784\ \text{m$^{3}$} \div 0.001\ \tfrac{\text{m$^{3}$}}{\text{L}} = 3.785411784\ \text{L}

    1 L = 0.001 m³, exact

  3. Combined factor

    1 gal=0.0037854117840.001 L=3.785411784 L1\ \text{gal} = \frac{0.003785411784}{0.001}\ \text{L} = 3.785411784\ \text{L}

    Both units are defined exactly and the converted value is a terminating decimal, so every digit shown in it is exact.

About the volume converter

Each volume unit is a fixed number of cubic metres. The US units are exact because they are built on the 1959 inch: a US gallon is 231 in³, which is 3.785411784 L. The imperial gallon is a different, larger unit, fixed by the UK Weights and Measures Act 1985 at exactly 4.54609 L.

The default converts 1 US gallon to 3.785411784 litres. Recipes and drink sizes are the other common use: a US cup is 1/16 gallon, 236.5882365 mL, and a US tablespoon is 3 teaspoons, 14.787 mL.

Choose the US or imperial version of a unit on purpose. An imperial pint (568 mL) is 20% larger than a US pint (473 mL), while an imperial fluid ounce (28.41 mL) is smaller than a US one (29.57 mL).

Worked examples

1 US gallon to litres

Value
1 gal
From
US gallon (gal)
To
litre (L)
Converted value
3.785411784 L
Exactness
Exact

Checked against: US gallon = 231 in³ × (0.0254 m)³ = 3.785411784 L (NIST HB 44 App. C); Python 3.8 fractions from the legal definitions

1 US gallon in cubic inches

Value
1 gal
From
US gallon (gal)
To
cubic inch (in³)
Converted value
231 in³

Checked against: NIST HB 44 App. C: 1 US gallon = 231 in³

Imperial gallon in US gallons

Value
1 gal (UK)
From
imperial gallon (gal (UK))
To
US gallon (gal)
Converted value
1.2009499255 gal

Checked against: 4.54609 L (UK Weights and Measures Act 1985) ÷ 3.785411784 L = 568261250/473176473 (Python 3.8 fractions from the legal definitions)

1 US tablespoon in teaspoons

Value
1 tbsp
From
US tablespoon (tbsp)
To
US teaspoon (tsp)
Converted value
3 tsp
Exactness
Exact

Checked against: NIST HB 44 App. C: 1 tablespoon = 3 teaspoons

Questions

How many litres are in a gallon?

A US gallon is exactly 3.785411784 L and an imperial (UK) gallon exactly 4.54609 L, 20% more. The US gallon is defined as 231 cubic inches; the imperial gallon was first defined in 1824 as the volume of 10 lb of water and is now fixed in litres by the UK Weights and Measures Act 1985.

How many millilitres are in a cup?

A US customary cup is 236.5882365 mL, 1/16 of a US gallon. US nutrition labels use a rounded 240 mL cup (21 CFR 101.9), and the metric cup used in Australia and New Zealand is 250 mL. The gap between 236.6 and 250 mL is about 6% of a cup, enough to matter in baking.

Is a UK pint bigger than a US pint?

Yes, by 20%. An imperial pint is 20 imperial fluid ounces, 568.26125 mL; a US liquid pint is 16 US fluid ounces, 473.176473 mL. The fluid ounces differ as well, 28.4130625 mL against 29.5735295625 mL, so a UK pint of beer is 1.2 US pints.

How many millilitres are in a tablespoon?

A US tablespoon is 14.78676478125 mL, half a US fluid ounce and exactly 3 teaspoons. The metric tablespoon is 15 mL, the figure US nutrition labels also round to. Australia's tablespoon is 20 mL (4 teaspoons), so an Australian spoonful holds 35% more than a US one.

How many litres are in a barrel of oil?

Exactly 158.987294928 L. An oil barrel is 42 US gallons, and 42 × 3.785411784 L gives that figure, about 0.159 m³. Oil production and prices use this barrel; a US beer barrel is 31 gallons, so check which barrel a source means.

How accurate is the volume converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 5 worked examples whose answers come from independent sources; for example, “1 US gallon to litres” is checked against US gallon = 231 in³ × (0.0254 m)³ = 3.785411784 L (NIST HB 44 App. C); Python 3.8 fractions from the legal definitions.

Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement.

About this calculator

xto=xfrom×ffromftof=one unit expressed in m3\begin{gathered} x_{\text{to}} = x_{\text{from}} \times \dfrac{f_{\text{from}}}{f_{\text{to}}} \\ f = \text{one unit expressed in } \text{m$^{3}$} \end{gathered}

Sources

  1. NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors
  2. NIST Handbook 44, Appendix C — General tables of units of measurement

Checked against references

5 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.

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