Divide gallons by 7.48
One cubic foot equals exactly 7.48052 US gallons, so dividing by 7.48 converts gallons to cubic feet. The factor is not a rounded convenience: a cubic foot is 1,728 cubic inches and a US gallon is 231, and 1,728 ÷ 231 = 7.48. For rough work, 7.5 is close enough.
Common conversions
| US gallons | Cubic feet |
|---|---|
| 50 gal | 6.68 ft³ |
| 100 gal | 13.37 ft³ |
| 500 gal | 66.84 ft³ |
| 1,000 gal | 133.68 ft³ |
| 5,000 gal | 668.4 ft³ |
| 10,000 gal | 1,336.8 ft³ |
To size a tank the other way, find its volume in cubic feet (length × width × height in feet) and multiply by 7.48: an 8 × 6 × 5 ft tank is 240 ft³, or about 1,795 gallons.
US versus imperial gallons
The word "gallon" means two different volumes. Using the wrong factor puts your answer off by a fifth.
The imperial gallon is about 20% bigger, so a cubic foot is 7.48 US gallons but only 6.23 imperial.
Common questions
How many gallons are in a cubic foot?
A cubic foot holds 7.48 US gallons. To go the other way, one gallon is 0.1337 cubic feet.
Where does the 7.48 factor come from?
A cubic foot is 1,728 cubic inches and a US gallon is 231 cubic inches. Dividing 1,728 by 231 gives 7.48052, an exact ratio rather than a rounded figure.
Is a UK gallon different?
Yes. An imperial (UK) gallon is about 20% larger, so a cubic foot holds only 6.23 imperial gallons instead of 7.48 US gallons. Check which gallon you are using before converting.
