The formula
US gal = m³ × 264.1720524
Where the factor comes from — each unit by its definition, then its size in SI:
1 m³ is the SI unit of volume.1 US gal = 231 × in³ = 0.003785411784 m³
Dividing the two SI sizes gives the factor: 264.172052358 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.003785411784.
The cubic metre is the SI unit of volume; the litre is exactly one thousandth of it. The US and UK gallons are different sizes, which is why a fuel-economy figure in mpg depends on which country printed it.
Worked examples
- A soft-drink bottle (2 L): 0.002 m³ = 0.528344 US gal — 0.002 × 264.1720524 = 0.528344
- A paint bucket: 0.0189271 m³ = 5 US gal — 0.0189271 × 264.1720524 = 5
- A water tank: 1 m³ = 264.172 US gal — 1 × 264.1720524 = 264.172
- A drinks can (330 mL): 0.00033 m³ = 0.0871768 US gal — 0.00033 × 264.1720524 = 0.0871768
Frequently asked questions
How many US gallons is 1 m³?
1 m³ = 264.172052358 US gal.
How do I convert US gallons back to cubic metres?
Divide by 264.172052358 — or multiply by 0.003785411784: 1 US gal = 0.003785411784 m³.