Volume converter guide
A litre is exactly one cubic decimetre, and one millilitre equals one cubic centimetre. This calculator uses litres as the common base for liquid-capacity and cubic-volume units.
US liquid and imperial units with similar names are different sizes. Every customary option is labeled with its system. US dry measures belong to the separate dry-volume converter and are intentionally excluded here.
How to convert volume units
- Enter the volume: Provide a finite, non-negative amount.
- Choose the source system: Select metric, US liquid, imperial, or cubic customary units.
- Choose the target: Select the result unit or reverse the pair with Swap.
- Convert: Select Convert volume to calculate through litres.
Formula and variables
The source is converted to litres before division by the target factor.
target volume = source volume × (litres per source unit) ÷ (litres per target unit)- Vₛ — Source volume
- A finite, non-negative volume.
- fₛ — Source factor
- Litres represented by one source unit.
- fₜ — Target factor
- Litres represented by one target unit.
Convert one US gallon to litres
Express one US liquid gallon in metric volume.
- Amount
- 1
- From
- gal (US)
- To
- L
- 1 US gallon = 231 in³
- 231 × 0.016387064 L/in³
Result: 1 US liquid gallon = 3.785411784 L.
An imperial gallon is larger and must not be substituted for the US value.
Understanding your results
System labels
US and imperial fluid ounces, pints, quarts, and gallons have different sizes. Retain the system label with the number.
Volume versus mass
Litres and gallons measure volume. Converting them to kilograms or pounds requires the material density.
Assumptions
- One litre is exactly 1 dm³.
- One cubic inch is exactly 0.016387064 L.
- One US liquid gallon is exactly 231 in³.
- One imperial gallon is exactly 4.54609 L.
Limitations
- US dry volume measures are not included.
- The calculator does not convert volume to mass without density.
- Recipe cups can follow conventions other than the US customary cup.
- Measurement uncertainty remains after unit conversion.
Common mistakes
- Treating US and imperial gallons as equal.
- Using a dry pint factor for liquid volume.
- Assuming every cup is 240 or 250 mL.
- Converting volume directly to weight without density.
- Rounding the gallon factor before completing the calculation.
Practical use cases
Cooking and liquid capacity
Compare explicitly labeled metric, US liquid, and imperial containers or recipes.
Cubic measurements
Convert in³, ft³, yd³, cm³, m³, and litres for spatial capacity.
Planning and decision guide
Confirm the measurement system
When a source says only gallon, pint, cup, or fluid ounce, identify its system before converting. The same unit name can represent different volumes.
Frequently asked questions
How many litres are in one US gallon?
One US liquid gallon is exactly 3.785411784 L.
How many litres are in one imperial gallon?
One imperial gallon is exactly 4.54609 L.
Is one millilitre equal to one cubic centimetre?
Yes. Both equal exactly 0.001 L.
Are US and imperial fluid ounces equal?
No. A US fluid ounce is 29.5735295625 mL; an imperial fluid ounce is 28.4130625 mL.
Can litres be converted directly to kilograms?
Not without density. Litres measure volume and kilograms measure mass.
Sources and review
- NIST Guide to the SI, Appendix B.9: Volume conversion factors — National Institute of Standards and Technology. Accessed 2026-08-30.
- NIST Handbook 44, current edition — National Institute of Standards and Technology. Accessed 2026-08-30.
Reviewed 2026-08-30.