How many gallons in a cubic foot?
1 cubic foot = 7.4805 US gallons (or 6.2288 UK gallons, or 28.317 litres). That figure comes from two exact definitions: the foot (0.3048 m, NIST) and the US gallon (3.785411784 L, NIST). Divide one by the other and you get 7.480519480... gallons per cubic foot — usually rounded to 7.48 for quick estimates.
Need to convert a specific volume right now? Use the cubic feet to gallons calculator → Enter any volume unit and get all the others instantly.
1. Where the 7.48 figure comes from
The conversion is an exact derivation from two international standards, not an approximation:
- 1 foot = 0.3048 metres (exact, defined 1959 by the International Yard and Pound Agreement and codified in NIST SP 811).
- 1 cubic foot = 0.3048³ = 0.028316846592 m³, which equals 28.316846592 litres (since 1 m³ = 1,000 L exactly).
- 1 US liquid gallon = 231 cubic inches (defined 1707, unchanged). Since 1 inch = 0.0254 m exactly, 231 in³ = 231 × (0.0254)³ m³ = 0.003785411784 m³ = 3.785411784 litres (exact).
Dividing: 28.316846592 ÷ 3.785411784 = 7.480519480... US gallons per cubic foot. This is irrational (the decimal never terminates), so every table and calculator rounds it — 7.48, 7.481, or 7.4805 depending on precision needed.
The UK gallon is different: the imperial gallon was redefined as exactly 4.54609 litres in 1985 (Weights and Measures Act), giving 28.316846592 ÷ 4.54609 = 6.228835459 UK gallons per cubic foot — about 16.7% larger than the US equivalent, which trips up a lot of trade estimates that mix the two.
2. Cubic feet to gallons — lookup table
All values are exact to the precision shown. For intermediate values, use the calculator.
| Cubic feet | US gallons | UK gallons | Litres |
|---|---|---|---|
| 0.5 ft³ | 3.74 | 3.11 | 14.16 |
| 1 ft³ | 7.48 | 6.23 | 28.32 |
| 2 ft³ | 14.96 | 12.46 | 56.63 |
| 5 ft³ | 37.40 | 31.14 | 141.58 |
| 7.35 ft³ | 54.98 | 45.78 | 208.13 |
| 10 ft³ | 74.81 | 62.29 | 283.17 |
| 13.37 ft³ | 99.99 | 83.28 | 378.60 |
| 20 ft³ | 149.61 | 124.58 | 566.34 |
| 27 ft³ (1 yd³) | 201.97 | 168.18 | 764.55 |
| 50 ft³ | 374.03 | 311.44 | 1,415.84 |
| 100 ft³ | 748.05 | 622.88 | 2,831.68 |
The 7.35 ft³ row is the volume of a standard 55-US-gallon drum (55 ÷ 7.4805 = 7.352 ft³ exactly; the table uses the rounded 7.35 ft³ input, so the US gal column shows 54.98 rather than 55). The 13.37 ft³ row is ≈ 100 US gallons — useful for tank sizing.
3. How to convert cubic feet to gallons by hand
The formula is straightforward:
US gallons = cubic feet × 7.4805
UK gallons = cubic feet × 6.2288
Litres = cubic feet × 28.317
To go the other way — gallons to cubic feet — divide instead of multiply:
Cubic feet = US gallons ÷ 7.4805
Cubic feet = UK gallons ÷ 6.2288
Cubic feet = litres ÷ 28.317
If you only remember one number, remember 7.48. It is close enough for ordering, quoting and field estimates. Where precision matters — tank specifications, permit drawings, pump curves — use the full 7.4805.
4. Practical examples
Pool volume
A rectangular in-ground pool that is 30 ft long, 15 ft wide and 5 ft deep has a volume of 30 × 15 × 5 = 2,250 ft³. Multiplied by 7.4805 gives 16,831 US gallons. That is roughly 63,700 litres — important for sizing the pump, heater and chemical dosing. The pool volume calculator handles sloped floors and round pools too.
Storage tanks
A vertical cylindrical tank 4 ft in diameter and 8 ft tall has a volume of π × 2² × 8 = 100.53 ft³ = 752 US gallons. Knowing this before you order the tank, the fill pump and the venting prevents three separate return trips to the supplier. The same math applies to water heater tanks, propane cylinders, septic tanks and holding tanks.
55-gallon drums and IBC totes
A standard 55-US-gallon drum holds 55 ÷ 7.4805 = 7.35 ft³. A 275-gallon IBC tote holds 275 ÷ 7.4805 = 36.76 ft³. When a delivery bay or equipment room is specified by square footage but your drums are spec'd in gallons, these conversions tell you exactly how many will fit.
Concrete and aggregate
Concrete is sold in cubic yards or cubic metres, but water content is often specified in gallons per cubic yard of mix. 1 cubic yard = 27 ft³ = 201.97 US gallons. So a mix design calling for 30 gallons of water per cubic yard is using 30 ÷ 201.97 = 14.9% of the yard's volume as water — a useful check when site conditions force you to adjust. See the concrete calculator for full pour volumes in both units.
Rainwater harvesting
Roof catchment area × rainfall depth gives volume in ft³ if your measurements are in feet. A 1,500 ft² roof collecting 1 inch of rain (1 in = 1/12 ft) captures 1,500 × (1/12) = 125 ft³ =935 US gallons. Most homeowners are surprised how much a single storm yields — and how large a storage tank actually needs to be to buffer a dry month.
5. US gallons vs UK gallons — the common mistake
The two gallon definitions differ by 20.1%: 1 UK gallon = 4.54609 L; 1 US gallon = 3.785411784 L. That gap is large enough to cause real errors. A pump rated for 50 UK gal/min pumps the same flow as a US-market pump rated at about 60 US gal/min. A hot water tank labelled as "200 litre" in a UK spec sheet holds only about 52.8 US gallons — not 52.8 UK gallons (which would be 240 litres). Anytime you see "gallons" in a document, verify which gallon is meant before plugging it into a formula.
The safest habit is to work in litres when mixing UK and US sources, converting to the local gallon only at the final output stage. The calculator above does exactly that — every intermediate calculation runs in litres, and all gallon variants are derived from the same litre value.
Common questions
- How many gallons are in a cubic foot?
- 1 cubic foot = 7.4805 US gallons (liquid). The exact value is 7.480519480... — from the NIST definitions of the foot (0.3048 m) and the US gallon (3.785411784 L).
- How many cubic feet is 100 gallons?
- 100 US gallons = 13.368 cubic feet. Divide gallons by 7.4805 to convert. 100 ÷ 7.4805 = 13.368 ft³.
- How many gallons is a 10 × 10 × 10 foot room?
- A 10 × 10 × 10 ft room = 1,000 ft³ = 7,480.5 US gallons of volume. That is about 28,317 litres (1,000 × 28.317 L/ft³).
- How many UK (imperial) gallons in a cubic foot?
- 1 cubic foot = 6.2288 UK (imperial) gallons. The UK gallon is larger than the US gallon: 4.54609 L vs 3.785411784 L.
- How do I calculate gallons from cubic feet?
- Multiply the volume in cubic feet by 7.4805 to get US gallons. For UK gallons, multiply by 6.2288. For litres, multiply by 28.317.
Last reviewed 2026-08.