Square Feet to Gallons Calculator
Turn a surface area into gallons of water. Enter the area in square feet and the depth in inches or feet, and get US gallons, cubic feet, and liters — for pools, ponds, stock tanks, or flooded floors.
Example: with Surface area (sq ft) 200 · Depth 12 · Depth unit inches → US gallons: 1,496 gallons.
- Cubic feet200.0 cu ft
- Liters5,663 L
Computed by the calculator below using its default values. Change any input to see your own numbers.
Gallons = square feet × depth in feet × 7.4805, because one cubic foot holds 7.4805 US gallons. Every inch of depth adds 0.62 gal per square foot.
Area alone is not a volume
Square feet measure a surface; gallons measure what sits on it, so you always need a depth. The bridge is the cubic foot: multiply area by average depth in feet, then by 7.4805 gallons per cubic foot. A 200 sq ft pond averaging 12 inches deep holds 200 cubic feet, just under 1,500 gallons.
The per-inch version is worth memorizing: one inch of water over one square foot is 0.623 gallons. That is how rain math works too — a 1,000 sq ft roof sheds about 623 gallons per inch of rain — and how you can size a flooded-basement pump: 800 sq ft under 2 inches of water is roughly 1,000 gallons.
How it’s calculated
Volume (cu ft) = area (sq ft) × depth (ft), with inches converted at 12 in = 1 ft. Gallons = cubic feet × 7.480519 (1 US gallon = 231 cu in exactly, so 1 cu ft = 1728 ÷ 231 = 7.48052 gal). Liters at 1 gal = 3.785411784 L exactly (NIST).
Uses average depth over the whole area — sloped pool bottoms and dished ponds should use the average of shallow and deep ends, not the maximum.
Gallons per square foot by depth
| Water depth | Gallons per sq ft | 1,000 sq ft holds |
|---|---|---|
| 1 in | 0.62 | 623 gal |
| 6 in | 3.74 | 3,740 gal |
| 12 in | 7.48 | 7,481 gal |
| 24 in | 14.96 | 14,961 gal |
| 48 in | 29.92 | 29,922 gal |
Computed with gallons = depth (ft) × 7.480519 per sq ft; rounded.
Common mistakes
- Forgetting depth entirely and hunting for a square-feet-to-gallons factor — no such constant exists without it.
- Entering depth in inches but selecting feet, which multiplies the answer by 12.
- Using maximum depth for a sloped pool instead of average depth (shallow + deep ÷ 2 for a straight slope).
- Expecting paint coverage from this tool: paint is spread thin, not pooled — figure about 350 sq ft per gallon instead.
Frequently asked questions
How do I convert square feet to gallons?
Multiply square feet by the water depth in feet, then by 7.4805. Formula: gallons = area × depth (ft) × 7.4805. With depth in inches, divide the inches by 12 first.
How many gallons is 1 inch of water per square foot?
0.623 gallons. Handy for rain harvesting: each inch of rain on 1,000 sq ft of roof is about 623 gallons.
How many gallons are in a cubic foot?
7.48052 US gallons. It follows from definitions: a gallon is exactly 231 cubic inches and a cubic foot is 1,728, so 1728 ÷ 231 = 7.48.
Does this work for paint or sealer coverage?
No — coatings are spread in a film, not filled by depth. Use the manufacturer's coverage rate, typically 250–400 sq ft per gallon for paint and 80–120 for driveway sealer.
How do I handle a pool with a shallow and deep end?
Use the average depth: (shallow + deep) ÷ 2 for a uniform slope. A 3 ft to 8 ft pool averages 5.5 ft, so a 15 × 30 pool holds about 450 × 5.5 × 7.48 ≈ 18,500 gallons.