How it works
The calculator works out the water surface area for the shape you pick, multiplies it by the average water depth, and converts the result to gallons and liters.
Rectangle: Surface = Length × Width
Round: Surface = π × (Diameter ÷ 2)²
Oval: Surface = (Length − Width) × Width + π × Width² ÷ 4
Ellipse: Surface = π ÷ 4 × Length × Width
Average depth = (Shallow end + Deep end) ÷ 2
Volume = Surface × Average depth; gallons = cubic feet × 7.48
The oval formula is a rectangle with a half circle on each end – the shape of most above-ground oval pools. A true ellipse of the same size holds less. The 7.48 gallons per cubic foot comes from the NIST definitions of the US gallon (231 cubic inches) and the foot; one cubic meter is 1,000 liters. Units are converted internally, so feet, inches and meters can be mixed.
Worked example
Inputs
- Pool shape
- Rectangle or square
- Length
- 32 ft
- Width
- 16 ft
- Shallow end water depth
- 3 ft 6 in ft
- Deep end water depth
- 6 ft
Result
- Water volume
- 18,193 gal (2,432 cu ft)
- In the other unit system
- 68,867 L (68.87 m³)
- Average depth
- 4.75 ft (57 in)
- Water surface area
- 512 sq ft
Common mistakes
- Using the wall height instead of the water depth. Above-ground pools are filled below the top of the wall, so a 52 in wall does not hold 52 in of water.
- Measuring the outside of the pool. Use the inside dimensions at the water line.
- Treating an above-ground oval pool as an ellipse. Most have straight sides and round ends, which hold more water than an ellipse of the same length and width – choose the matching shape.
- Averaging the depths of a pool with a steep break or a diving well. Split it into sections with even floors and add their volumes.
Assumptions and limits
- The pool walls are vertical and the floor slopes evenly between the shallow and deep ends; the average depth is the mean of the two.
- Oval means two straight sides with a half circle at each end; the shorter dimension is the width. Ellipse means a true elliptical outline.
- Volumes are converted with 1 cubic foot = 1,728 ÷ 231 ≈ 7.48 US gallons and 1 cubic meter = 1,000 liters (NIST). Steps, benches and coves are not subtracted.
- Kidney and free-form shapes are not offered because there is no exact formula for them – split them into rectangles and circles, or use the pool maker’s stated capacity.
Frequently asked questions
How do I calculate how many gallons are in my pool?
Multiply the length by the width by the average depth in feet to get cubic feet, then multiply by 7.48. A 32 × 16 ft pool that runs from 3 ft 6 in to 6 ft deep averages 4.75 ft, so 32 × 16 × 4.75 = 2,432 cubic feet, or about 18,193 gallons.
How many gallons is a round pool?
Multiply π × radius² × depth to get cubic feet, then by 7.48. A 24 ft round pool with 4 ft of water holds π × 12² × 4 = 1,810 cubic feet, about 13,536 gallons.
How do I find the average depth of a pool?
Add the water depth at the shallow end and at the deep end and divide by two. That works when the floor slopes evenly; for a pool with a sudden drop, work out the shallow and deep sections separately.
How many liters is my pool?
Work out the volume in cubic meters (length × width × average depth in meters) and multiply by 1,000. A 10 × 5 m pool from 1 m to 2 m deep holds 10 × 5 × 1.5 = 75 m³, or 75,000 liters.
How many gallons are in a cubic foot of water?
7.48 US gallons. A US gallon is defined as 231 cubic inches and a cubic foot is 1,728 cubic inches, so 1,728 ÷ 231 = 7.4805.
Sources
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 6, 2026