Cubic feet to gallons
Multiply by 7.48052. Exact, from the gallon's definition.
Material estimate
Enter a figure in cubic feet.
You need to buy
Use this figure
Worth knowing
What this assumes
Seven point four eight, and where it comes from
The US liquid gallon is defined as exactly 231 cubic inches. A cubic foot is 12 × 12 × 12 = 1,728 cubic inches. Divide one by the other and you get 7.48052 gallons to the cubic foot — an exact consequence of two definitions rather than anything anybody measured.
Rounding it to 7.5 is under a third of a per cent out and fine for filling a pool. For sizing a pump or dosing chemicals by the gallon, use the full figure.
US or imperial matters more than you would think
An imperial gallon is about 20 per cent larger than a US one — 4.546 litres against 3.785. So a cubic foot is 7.48 US gallons and only 6.23 imperial. Equipment specified in one and bought against the other is a real and common error on anything imported, and it is always in the direction of the tank being smaller than you thought.
Cubic feet in gallons, both kinds, and what the water weighs
| Cubic feet | US gallons | Imperial gallons | Weight of water (lb) |
|---|---|---|---|
| 1 ft³ | 7.48 | 6.23 | 62.4 |
| 10 ft³ | 74.81 | 62.29 | 624.2 |
| 27 ft³ | 201.97 | 168.18 | 1685.5 |
| 100 ft³ | 748.05 | 622.88 | 6242.5 |
| 500 ft³ | 3740.26 | 3114.42 | 31212.5 |
| 1,000 ft³ | 7480.52 | 6228.84 | 62424.9 |
| 2,500 ft³ | 18701.3 | 15572.09 | 156062.3 |
Exact volume conversions. Water weight is at about 8.34 lb a US gallon, which varies slightly with temperature — enough to notice on a tank, not enough to matter on a pool.
Where this goes next
For a pool the volume itself is the hard part, because the floor slopes — the pool volume calculator averages the shallow and deep ends rather than taking one depth, which is where home-made estimates go wrong by a third. For a hole or a tank you are digging for, the cubic yard calculator turns a shape into a volume and the excavation calculator adds the swell that decides how many truck loads leave the site. The reverse of this page is gallons to cubic feet.
Common questions
How many gallons are in a cubic foot?
7.48052 US liquid gallons. The gallon is defined as exactly 231 cubic inches, and a cubic foot is 1,728 cubic inches, so the factor falls straight out of the two definitions. It is exact rather than measured.
How do I convert cubic feet to gallons?
Multiply by 7.48052. Most people round it to 7.5, which is under a third of a per cent out and perfectly good for a pool or a tank — but if you are sizing a pump or buying chemicals by the gallon, use the full figure.
Is that a US gallon or an imperial gallon?
US liquid. An imperial gallon is about 20 per cent larger — 4.546 litres against 3.785 — so a cubic foot is 7.48 US gallons but only 6.23 imperial. A British spec sheet and an American tank are genuinely not talking about the same unit, and the table below gives both.
How many gallons is my pool?
Work out the volume in cubic feet first, then multiply. The catch on a pool is that most of them have a sloping floor, so the depth is not one number — the pool volume calculator averages the shallow and deep ends properly, which is where most home-made estimates go wrong by a third.
What does a gallon of water weigh?
About 8.34 pounds at room temperature, so a cubic foot of water is roughly 62.4 pounds — which is the figure the asphalt page uses to turn a specific gravity into a unit weight. The last column of the table gives the weight, and it matters more often than people expect: a 500 gallon tank is over two tons of water before you count the tank.