The formula
L = ft³ × 28.316846592
Where the factor comes from — each unit by its definition, then its size in SI:
1 ft³ = ft³ = 0.028316846592 m³1 L = m³ / 1000 = 0.001 m³
Dividing the two SI sizes gives the factor: 28.316846592, exact — every step above is a definition, not a measurement. The reverse factor is 0.0353146667215.
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: 0.0706293 ft³ = 2 L — 0.0706293 × 28.31684659 = 2
- A paint bucket (5 US gal): 0.668403 ft³ = 18.9271 L — 0.668403 × 28.31684659 = 18.9271
- A water tank (1 m³): 35.3147 ft³ = 1,000 L — 35.3147 × 28.31684659 = 1,000
- A drinks can (330 mL): 0.0116538 ft³ = 0.33 L — 0.0116538 × 28.31684659 = 0.33
Frequently asked questions
How many litres is 1 ft³?
1 ft³ = 28.316846592 L, exactly, from the unit definitions.
How do I convert litres back to cubic feet?
Divide by 28.316846592 — or multiply by 0.0353146667215: 1 L = 0.0353146667215 ft³.