How to convert cubic feet to gallons
One cubic foot holds 7.48052 US liquid gallons. The factor comes from the definition: 1 US gallon = 231 in³, and 1 ft³ = 1,728 in³, so 1,728 ÷ 231 ≈ 7.48052 gallons per cubic foot.
Worked examples
Example 1: A 50-gallon water heater
50 ÷ 7.48052 ≈ 6.68 ft³ of internal volume.
Example 2: A 4 × 8 × 4 ft swimming pool section
4 × 8 × 4 = 128 ft³ × 7.48052 ≈ 957.5 US gallons.
Example 3: A 1,000 ft³ residential water tank
1,000 × 7.48052 ≈ 7,481 US gallons.
| Cubic feet → US gallons | Conversion factor | Worked example |
|---|---|---|
| 1 ft³ | × 7.48052 | 7.48 gal |
| 5 ft³ | × 7.48052 | 37.40 gal |
| 10 ft³ | × 7.48052 | 74.81 gal |
| 100 ft³ | × 7.48052 | 748.05 gal |
| 1,000 ft³ | × 7.48052 | 7,481 gal |
Common uses
- Water tank, cistern, and rain barrel capacity
- Swimming pool, hot tub, and spa volume
- Aquarium volume conversions
- Drainage and stormwater calculations
- Heating oil and water heater capacity
Where this conversion comes up
Gallons is the standard for liquid volume in the US, especially for tanks, pools, and aquariums. Almost any time water is the subject, you will end up converting cubic feet to gallons.
- Swimming pools — chemical doses are calculated per gallon, not per cubic foot.
- Water tanks and rain barrels — capacity is always quoted in gallons.
- Aquariums, hot tubs, and koi ponds — every spec sheet is in gallons.
- Septic tank sizing and well-water reserve calculations.
Common mistakes to avoid
- Confusing US and UK gallons. 1 ft³ = 7.48052 US gallons, but 6.22884 UK (imperial) gallons. International recipes and product specs sometimes use UK gallons.
- Confusing US liquid and US dry gallons. The factor 7.48052 is for US liquid gallons. US dry gallons (used for grain and produce) are different.
- Forgetting that gallons measure liquids only. Volumes of solids (sand, soil, gravel) can technically be expressed in gallons, but the convention is to use cubic feet or cubic yards instead.
Expert tips
- Multiply cubic feet by 7.48052 for US liquid gallons. Quick mental math: ft³ × 7.5 gets you very close. A 100-gallon fish tank ≈ 13.4 ft³.
- For pool chemistry, gallons is the standard unit. Chlorine, salt, and pH adjusters are dosed per gallon. Calculate pool volume in cubic feet, then convert. See the swimming pool calculator.
- For propane and natural gas, gallons applies to the liquid form only. Vapor-phase gas is measured in cubic feet (or BTU). The 7.48052 factor is for liquid water. See the cubic feet to BTU converter for gas applications.
- Round to whole gallons for everyday use. A 75 ft³ tank holds 561.04 gallons — call it 561 for ordering, 561.04 for engineering math.
Frequently asked questions
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