A cubic foot contains 7.48052 US liquid gallons, so for everyday use, the quick answer is about 7.48 US gallons of liquid. Practically speaking, 5 gallons per cubic foot**. More precisely, **1 cubic foot = 7.This conversion is useful for water tanks, aquariums, pools, irrigation, fuel storage, construction estimates, and any situation where volume is measured in cubic feet but capacity is described in gallons The details matter here..
The Short Answer
If you are asking how many gallons are in a cubic foot, the standard answer in the United States is:
1 cubic foot = 7.48 US gallons
That means:
- 1 ft³ = 7.48052 gallons
- 2 ft³ = 14.961 gallons
- 5 ft³ = 37.403 gallons
- 10 ft³ = 74.805 gallons
For most practical calculations, you can multiply cubic feet by 7.48 to get US gallons It's one of those things that adds up..
Why There Are 7.48 Gallons in a Cubic Foot
A cubic foot is a unit of volume. It represents the space inside a box that is 1 foot long, 1 foot wide, and 1 foot high.
Since there are 12 inches in 1 foot, a cubic foot equals:
12 inches × 12 inches × 12 inches = 1,728 cubic inches
A US liquid gallon is defined as exactly 231 cubic inches. To find out how many gallons fit into one cubic foot, divide the number of cubic inches in a cubic foot by the number of cubic inches in a gallon:
1,728 ÷ 231 = 7.48052
That is why one cubic foot holds about 7.48 US gallons.
US Gallons vs. Imperial Gallons
The answer can change depending on whether you are using US gallons or Imperial gallons.
In the United States, gallons usually refer to US liquid gallons. That said, the Imperial gallon is used in some countries and is larger than the US gallon The details matter here..
| Measurement System | Gallons in 1 Cubic Foot |
|---|---|
| US liquid gallon | 7.48052 gallons |
| Imperial gallon | 6.22884 gallons |
So, if you are working with US measurements, use 7.48 gallons per cubic foot. This leads to if you are working with Imperial gallons, use 6. 23 gallons per cubic foot Not complicated — just consistent..
How to Convert Cubic Feet to Gallons
To convert cubic feet to gallons, use this formula:
Gallons = Cubic Feet × 7.48052
Here's one way to look at it: if you have a container that holds 10 cubic feet, the calculation is:
10 × 7.48052 = 74.8052 gallons
So, a 10-cubic-foot container holds about 74.8 US gallons.
You can also use this simpler version for quick estimates:
Gallons ≈ Cubic Feet × 7.5
For example:
4 ft³ × 7.5 = 30 gallons
The exact answer would be **
29.92 gallons (4 × 7.48052 = 29.92208) Simple as that..
Quick Reference Conversion Table
| Cubic Feet (ft³) | US Gallons (Exact) | US Gallons (Rounded) |
|---|---|---|
| 1 | 7.48052 | 7.And 48 |
| 2 | 14. Think about it: 96104 | 14. 96 |
| 3 | 22.44156 | 22.In practice, 44 |
| 4 | 29. Day to day, 92208 | 29. 92 |
| 5 | 37.But 40260 | 37. And 40 |
| 6 | 44. 88312 | 44.And 88 |
| 7 | 52. 36364 | 52.Worth adding: 36 |
| 8 | 59. 84416 | 59.84 |
| 9 | 67.That's why 32468 | 67. Still, 32 |
| 10 | 74. 80520 | 74.Here's the thing — 81 |
| 20 | 149. Which means 61040 | 149. 61 |
| 50 | 374.In practice, 02600 | 374. 03 |
| 100 | 748.05200 | 748. |
Converting Gallons Back to Cubic Feet
If you know the capacity in gallons and need the volume in cubic feet, simply reverse the formula:
Cubic Feet = Gallons ÷ 7.48052
Or, for a quick estimate:
Cubic Feet ≈ Gallons ÷ 7.5
Example: A water heater is rated for 50 gallons. How many cubic feet of space does it occupy?
- Exact: 50 ÷ 7.48052 = 6.68 ft³
- Estimate: 50 ÷ 7.5 = 6.67 ft³
Calculating Volume for Common Shapes
Since the conversion starts with cubic feet, you first need to determine the volume of your container in ft³ Which is the point..
Rectangular Tank / Box / Room
Volume (ft³) = Length (ft) × Width (ft) × Height (ft)
Example: A tank 4 ft long, 2 ft wide, and 3 ft high. 4 × 2 × 3 = 24 ft³ 24 × 7.48052 = 179.53 gallons
Cylinder (Vertical or Horizontal Tank)
Volume (ft³) = π × Radius² × Height (or Length) (Radius = Diameter ÷ 2. Ensure all measurements are in feet.)
Example: A pipe 10 ft long with a 1 ft diameter (0.5 ft radius). 3.14159 × 0.5² × 10 = 7.85 ft³ 7.85 × 7.48052 = 58.72 gallons
Sphere
Volume (ft³) = (4/3) × π × Radius³
Practical Tips for Accuracy
- Measure Internal Dimensions: Always measure the inside length, width, and height. Wall thickness reduces the actual holding capacity.
- Account for "Dead Space": Pipes, fittings, pump intakes, and the curved bottom of some tanks take up volume that liquid cannot fill. Subtract this displacement if precision is critical.
- Temperature Matters: Water expands when heated. A "40-gallon" water heater actually holds slightly more than 40 gallons of cold water, but the rated capacity accounts for thermal expansion safety margins.
- Dry vs. Liquid Gallons: This article covers US liquid gallons. A US dry gallon (used for grain, berries, etc.) is different (≈ 0.86 dry gallons per cubic foot). Do not mix them up.
Conclusion
Whether you are sizing a sump pump, stocking an aquarium, calculating pool chemicals, or estimating concrete slurry, the relationship between cubic feet and gallons is a fundamental conversion to master. Remember the anchor number: 1 cubic foot = 7.48052 US gallons. Here's the thing — for mental math, 7. 5 gets you close enough for estimates; for purchasing chemicals, sizing equipment, or billing, use the precise 7.48052 multiplier. With the formulas and reference table above, you can move confidently between cubic feet and gallons for any project.
