Cubic Feet to Gallons Calculator
A cubic feet to gallons calculator multiplies cubic feet by 7.48052, since 1 cu ft = 1,728 in³ and a gallon is 231 in³. 100 cu ft equals about 748.1 US gallons.
How many gallons are in a cubic foot?
A cubic feet to gallons calculator multiplies the volume in cubic feet by 7.48052 to get US gallons, and by 28.3168 to get liters. The factor comes from how the units are defined: one cubic foot is 1,728 cubic inches (12 × 12 × 12), and one US gallon is exactly 231 cubic inches. 1,728 ÷ 231 = 7.48052. So 100 cubic feet holds about 748.1 gallons, or 2,831.7 liters.
Tanks, troughs, ponds, and pools are measured with a tape in feet, but pumps, chemical doses, and water bills all work in gallons. This conversion connects the two.
The formula in plain words
- Find the volume in cubic feet. For a box, that is length × width × depth. For a round tank, it is π × radius² × height.
- Gallons = cubic feet × 7.48052.
- Liters = cubic feet × 28.3168.
The calculator shows gallons and liters to one decimal place.
Worked examples
- 100 cubic feet (calculator default)
- Gallons: 100 × 7.48052 = 748.1 gal
- Liters: 100 × 28.3168 = 2,831.7 L
- A stock tank 8 ft long, 4 ft wide, filled 2.5 ft deep
- Volume: 8 × 4 × 2.5 = 80 cu ft
- Gallons: 80 × 7.48052 = 598.4 gal
- Liters: 80 × 28.3168 = 2,265.3 L
- Weight of the water: 598.4 × 8.34 lb ≈ 4,991 lb
A full tank that size weighs over two tons, far more than a typical deck is built to carry in one spot.
Cubic feet to gallons table
| Cubic feet | US gallons | Liters |
|---|---|---|
| 1 | 7.5 | 28.3 |
| 5 | 37.4 | 141.6 |
| 10 | 74.8 | 283.2 |
| 25 | 187.0 | 707.9 |
| 50 | 374.0 | 1,415.8 |
| 100 | 748.1 | 2,831.7 |
| 250 | 1,870.1 | 7,079.2 |
| 500 | 3,740.3 | 14,158.4 |
| 1,000 | 7,480.5 | 28,316.8 |
A handy check: 4 cu ft is just under 30 gallons, the size of a large trash can, and 27 cu ft (one cubic yard) is about 202 gallons.
How to get the cubic feet
- Rectangular tanks and troughs: length × width × water depth, all in feet. Use the inside dimensions.
- Round tanks: π × (diameter ÷ 2)² × height. The tank volume calculator does this and gives gallons directly.
- Measurements in inches: multiply the three inch dimensions together and divide by 1,728 to get cubic feet. Or skip cubic feet and divide cubic inches by 231 for gallons.
- Partly full containers: use the water depth, not the wall height.
- Odd shapes: split them into boxes and cylinders, add the cubic feet, then convert once.
Common mistakes
- Mixing inches and feet. A 24 in deep tank is 2 ft. Entering 24 as feet makes the result 12 times too big.
- Using outside dimensions. Thick walls on a concrete or poly tank can take a lot off the real capacity.
- Using 7.5 for big numbers. It is fine for a quick check, but on 10,000 cu ft it adds about 195 gallons.
- Confusing US and imperial gallons. The US gallon is about 17% smaller than the imperial one.
- Treating volume as weight. Gallons tell you how much fits, not how heavy it is. For water, multiply gallons by about 8.34 to get pounds, as in example 2.
Related conversions
To go the other way, use the gallons to cubic feet calculator, which multiplies gallons by 0.133681. For metric work, the gallons to liters calculator converts directly. To size a swimming pool from its length, width, and depth, the pool gallons calculator builds in this same 7.48 factor.
Frequently asked questions
How many gallons are in a cubic foot?
7.48052 US gallons. A cubic foot is 12 × 12 × 12 = 1,728 cubic inches, and a US gallon is defined as 231 cubic inches, so 1,728 ÷ 231 = 7.48052. For quick mental math, 7.5 gallons per cubic foot is within 0.3%.
Why measure a tank in cubic feet first?
Feet come straight off a tape measure. A 4 × 2 × 2 ft trough is 16 cu ft by simple multiplication, and 16 × 7.48052 = 119.7 gallons. Working in gallons from the start would mean juggling 231 cubic inches per gallon partway through.
How much does a cubic foot of water weigh?
About 62.4 lb. That is 7.48 gallons × roughly 8.34 lb per gallon. An 80 cu ft stock tank holds 598.4 gallons, which weighs close to 5,000 lb when full, before the tank itself, so check what it sits on.
Is the result different for other liquids?
Not for volume. 100 cu ft is 748.1 gallons whether it holds water, diesel, or grain. Weight is what changes: a gallon of water is about 8.34 lb, while lighter liquids weigh less per gallon. This calculator converts volume only.
Does this use US or imperial gallons?
US gallons. An imperial (UK) gallon is larger, about 4.546 liters versus 3.785, so one cubic foot is only about 6.23 imperial gallons. If a product label is from the UK or an older Canadian source, check which gallon it means.
Estimates only. Verify quantities with your supplier before purchasing.