gallons to cubic feet calculator
Convert US gallons to cubic feet and liters. Formula, worked example, and a reference table for tank and pool volume estimating.
Gallons measure the water or liquid a container holds; cubic feet measure the physical space it takes up. This calculator converts a gallon figure into cubic feet and liters, useful for checking tank ratings, sizing pumps, or matching a supplier’s gallon quote against a space measured in feet.
How this calculator works
A cubic foot holds 7.48052 US gallons, so one gallon equals the reciprocal of that figure in cubic feet.
Formula: Cubic feet = Gallons × 0.133681. Liters = Gallons × 3.78541.
Worked example
Enter 100 gallons, the calculator’s default:
- Cubic feet: 100 × 0.133681 = 13.368 cu ft
- Liters: 100 × 3.78541 ≈ 378.5 L
That’s roughly the volume of a small water heater or a compact rain barrel.
Reference
| Gallons | Cubic feet | Liters |
|---|---|---|
| 50 gal | 6.684 cu ft | ≈189.3 L |
| 100 gal | 13.368 cu ft | ≈378.5 L |
| 250 gal | 33.420 cu ft | ≈946.4 L |
| 500 gal | 66.841 cu ft | ≈1,892.7 L |
Where this conversion is used
Water tanks, propane tanks, and swimming pools are usually rated in gallons, but if you’re sizing an enclosure, calculating shipping weight, or checking a manufacturer’s stated capacity against measured dimensions, you need cubic feet. Going the other way — converting a tank’s measured cubic footage into the gallons it holds — use the Cubic Feet to Gallons Calculator, or size a full tank from scratch with the Tank Volume Calculator.
Frequently asked questions
How many cubic feet are in a gallon?
One US gallon equals 0.133681 cubic feet. That's because a cubic foot holds 7.48 gallons of water — the two units are reciprocals of each other.
Why do tank specs mix gallons and cubic feet?
Tank capacity is usually sold in gallons (a familiar consumer unit), but tank dimensions and shipping calculations are done in cubic feet. Converting between the two lets you check a manufacturer's gallon rating against the tank's measured dimensions.
Is this the US gallon or the UK imperial gallon?
This calculator uses the US gallon (3.78541 liters), the standard in US plumbing, tank, and pool specifications. The UK imperial gallon is about 20% larger (4.54609 liters) — check which one a spec sheet uses before ordering water treatment chemicals dosed by gallon.
How do I find the cubic feet of a rectangular tank?
Multiply length × width × height in feet. Compare that number to the gallons-to-cubic-feet result from a manufacturer's rated capacity — if they don't roughly match, the tank may not be rated the way you expect.
What's the reverse conversion?
Multiply cubic feet by 7.48052 to get gallons. Our Cubic Feet to Gallons Calculator handles that direction directly.
Estimates only. Verify quantities with your supplier before purchasing.