How many gallons is my pool?
Multiply length × width × average depth (in feet) and then multiply by 7.48 to get US gallons. A 12 × 24 ft rectangular pool with a 4 ft average depth holds 8,618 US gallons (32,621 litres). Round, oval and kidney pools use slightly different formulas — all covered below.
Prefer to skip the arithmetic? Use the pool volume calculator → Enter the shape, dimensions and depths — get the gallons and litres instantly.
1. Why pool volume matters
Pool volume is the one number that drives almost everything else in pool maintenance. Chemical dosing — chlorine, pH adjusters, algaecide, shock — is always expressed as an amount per 10,000 gallons (or per 10,000 litres in metric regions), so a wrong volume means a wrong dose: too low and the water goes green; too high and the chemistry can irritate eyes and skin.
Pump run time depends on volume too. Most pools need the entire water volume circulated at least once every 6–8 hours, so you divide the pool volume by the pump's flow rate in gallons (or litres) per hour to find how long to run it. Get the volume right and you avoid both under-filtering and wasted electricity.
Heaters and heat pumps are also sized by volume — the more water to warm, the more BTUs needed. Whether you are buying a new heater or troubleshooting why an existing one cannot keep up, pool volume is the starting point.
2. The average depth: the most important number to get right
Most swimming pools have a sloped floor that goes from a shallow end (typically 3–3.5 ft / 0.9–1.1 m) down to a deep end (typically 5–8 ft / 1.5–2.4 m). The volume formula uses a single average depth, not the deep end alone.
Average depth = (shallow end depth + deep end depth) ÷ 2. For a pool 3 ft at the shallow end and 5 ft at the deep end: (3 + 5) ÷ 2 = 4 ft. If your pool has a flat floor, just enter the same depth for both ends.
Using the deep end as the average — a common mistake — overstates the volume, sometimes by 25–30%. That leads to over-dosing chemicals and over-estimating heating costs.
3. Rectangular pool: the most common shape
The rectangular (or square) pool is the simplest to calculate:
Volume (ft³) = length × width × average depth
Volume (US gal) = ft³ × 7.48
Volume (litres) = ft³ × 28.317
Worked example — a 12 × 24 ft pool, 3 ft shallow end, 5 ft deep end:
- Average depth = (3 + 5) ÷ 2 = 4 ft
- Volume = 12 × 24 × 4 = 1,152 ft³
- Gallons = 1,152 × 7.48 = 8,618 US gal
- Litres = 1,152 × 28.317 = 32,621 L
The exact conversion is 1 US gallon = 231 cubic inches = 231 ÷ 1728 = 0.13368 ft³, so 1 ft³ = 1728 ÷ 231 = 7.48052 US gallons (exact, not an approximation — derived directly from the definition of the US gallon).
4. Round pool
A round (circular) pool has a circular cross-section. The area of a circle is π × r², where r is the radius (half the diameter):
Volume (ft³) = π × (diameter ÷ 2)² × average depth
Example — a round pool 14 ft across, 3.5 ft average depth:
- Radius = 14 ÷ 2 = 7 ft
- Volume = π × 7² × 3.5 = π × 49 × 3.5 = 538.8 ft³
- Gallons = 538.8 × 7.48052 = 4,030 US gal
- Litres = 538.8 × 28.317 = 15,257 L
Above-ground round pools often have a flat floor, so shallow and deep end depths are identical — just enter the same value for both.
5. Oval pool
An oval pool is treated as an ellipse. The area of an ellipse is π/4 × length × width (where length and width are the two axis measurements, not radii):
Volume (ft³) = (π ÷ 4) × length × width × average depth
Example — a 12 × 20 ft oval pool, 3.5 ft average depth:
- Volume = (π ÷ 4) × 12 × 20 × 3.5 = 0.7854 × 240 × 3.5 = 659.7 ft³
- Gallons = 659.7 × 7.48 = 4,934 US gal
- Litres = 659.7 × 28.317 = 18,682 L
6. Kidney-shaped pool
A kidney pool has two lobes — a narrower concave side (W1) and a wider convex side (W2). The standard industry approximation uses a factor of 0.45:
Volume (ft³) ≈ 0.45 × (W1 + W2) × length × average depth
The 0.45 factor accounts for the concave kidney outline — the pool is smaller than a simple rectangle of the same overall dimensions. It is approximate (not exact), and that is true of every kidney pool volume estimate because the exact shape varies by manufacturer and design.
Example — a kidney pool 20 ft long, 10 ft narrow side, 14 ft wide side, 4 ft average depth:
- Volume ≈ 0.45 × (10 + 14) × 20 × 4 = 0.45 × 24 × 80 = 864 ft³
- Gallons ≈ 864 × 7.48 = 6,463 US gal
- Litres ≈ 864 × 28.317 = 24,466 L
7. Pool volume reference table (rectangular pools)
Common rectangular pool sizes with typical sloped floors. Enter your own dimensions for an exact figure.
| Pool size (ft) | Avg depth | US gallons | Litres |
|---|---|---|---|
| 10 × 20 ft | 3.5 ft | 5,236 | 19,822 |
| 12 × 24 ft | 4 ft | 8,618 | 32,621 |
| 14 × 28 ft | 4 ft | 11,729 | 44,401 |
| 16 × 32 ft | 4.5 ft | 17,235 | 65,242 |
| 18 × 36 ft | 5 ft | 24,237 | 91,747 |
| 20 × 40 ft | 5 ft | 29,922 | 113,267 |
Metric pools
| Pool size (m) | Avg depth | Litres | US gallons |
|---|---|---|---|
| 3 × 6 m | 1.2 m | 21,600 | 5,706 |
| 4 × 8 m | 1.2 m | 38,400 | 10,144 |
| 5 × 10 m | 1.4 m | 70,000 | 18,492 |
| 6 × 12 m | 1.5 m | 108,000 | 28,531 |
8. How to use the pool volume in practice
Once you have the volume, it connects directly to the three main pool calculations:
Chemical dosing. Most pool chemicals state a dose per 10,000 US gallons (or per 10,000 litres). Divide your pool volume by 10,000 and multiply by the stated dose. So for a pool of 20,000 gallons, a chemical calling for 1 oz per 10,000 gallons needs 2 oz. Always check the product label — never guess a chemical dose.
Pump run time. Divide pool volume (gallons or litres) by pump flow rate (same units per hour) to get the hours needed for one full turnover. Most pools target one turnover every 6–8 hours, so if the pool is 20,000 gallons and the pump moves 50 GPH, that is 20,000 ÷ 50 = 400 hours — clearly wrong because GPH should be GPM × 60, so a pump rated 50 GPM delivers 3,000 GPH and turns 20,000 gallons over in 6.7 hours.
Heater sizing. A rough rule of thumb is that a heat pump or gas heater needs roughly 1 BTU to raise 1 gallon of water by 1°F (or 1 kJ to raise about 1 litre by 0.24°C). Multiply by the temperature rise you want and the hours you have to reach it — your pool or heater supplier can refine the figure for your climate and target temperature.
Common questions
- How many gallons is my pool?
- It depends on the shape and dimensions. For a rectangular pool, multiply length × width × average depth, then multiply by 7.48 to convert cubic feet to US gallons. A 12 × 24 ft pool with a 4 ft average depth is 12 × 24 × 4 = 1,152 ft³ × 7.48 = about 8,618 US gallons. Use the calculator for any shape — it handles rectangle, round, oval and kidney pools.
- How do I calculate the volume of a pool in gallons?
- Measure the length, width, shallow-end depth and deep-end depth. Average the two depths for pools with a sloped floor. Then apply the formula for your shape, multiply by 7.48 (cubic feet to US gallons) or by 28.317 (cubic feet to litres). The calculator on this site does all the arithmetic once you enter the dimensions.
- How many gallons are in a 12 × 24 pool?
- A 12 × 24 ft rectangular pool with a 3 ft shallow end and 5 ft deep end has an average depth of 4 ft. Volume = 12 × 24 × 4 = 1,152 ft³ = about 8,618 US gallons (32,621 litres). If your depths differ, enter them into the calculator.
- How do I calculate the volume of a kidney-shaped pool?
- Use the standard industry formula: Volume ≈ 0.45 × (W1 + W2) × length × average depth, where W1 is the narrower width across the concave side and W2 is the wider width across the convex side. This gives an approximate answer — the 0.45 factor accounts for the lobed kidney outline and is accepted as the industry standard for pool volume estimates.
- Why does my pool volume matter?
- Pool volume is the base number for calculating chemical doses — chlorine, pH adjusters, algaecide and shock all require a volume figure to get the dosing right. It also determines pump run time (most pools need the water turned over at least once every 6–8 hours), and it is the starting point for sizing a pool heater or heat pump.
Reference & education only. Not professional, engineering, or code-compliance advice. Estimates are based on published model codes; local amendments and your Authority Having Jurisdiction (AHJ) govern. Always verify against the current adopted code and a licensed professional before doing work.
Last reviewed 2026-07.