Pool Volume Calculator
Accurate pool capacity for US gallons, litres, and cubic feet.
Rectangular Pool Volume
Pool Owner Toolkit
Go beyond volume — get chemical dosing, fill time, cost estimates, and equipment recommendations.
Geometric Formulas
Pool volume calculations are based on geometric formulas for surface area. Each pool shape has a distinct surface area formula — apply it first, then multiply by depth and by 7.48 to get cubic volume in gallons.
Variable Legend
Area Formulas by Shape
A = L × W A = (L × W) ÷ 2 A = π × r² A = π × (L÷2) × (W÷2) Multiply surface area by depth to get cubic volume in cubic feet, then multiply by 7.48 to convert to US gallons (or use 7.5 as a quick approximation). For a round pool volume calculator, the circle formula above applies directly.
How to Calculate Pool Volume
Calculate surface area using the geometric formula for your pool shape (L × W for rectangular, π × r² for circular).
Multiply by average water depth to get cubic volume in cubic feet. When depth varies, average the shallow and deep ends.
Multiply cubic feet by 7.48 to convert to US gallons (7.5 for a quick estimate). The calculator above handles all shapes automatically.
Constant Depth Pools — Flat-Bottom Square and Rectangular
A 20 × 10 ft pool at 5 ft constant depth:
This formula applies to square pools and all inground rectangular pools with a flat bottom. If your pool has any slope from the shallow end to the deep end, use the variable depth method below.
See the rectangular pool volume calculator for step-by-step input fields.
Variable Depth Pools
Example: a pool length of 25 ft 9 in = 25 + (9 × 0.0833) = 25.75 ft
A pool 25.75 ft long × 10 ft wide × 6 ft average depth:
Two-Section Method
Use average depth when the bottom slope is gradual across the whole pool. If the shallow section is wide and flat and the deep section drops abruptly, treat the pool as two separate volumes. Calculate each section independently using its own length and depth, then add the two results together for a more accurate pool capacity calculation.
Depth Warning
Always measure water depth from the waterline down to the pool floor — not from the top of the pool wall. Using wall height instead of actual water depth overstates pool volume by up to 33%, which directly affects chemical dosing accuracy.
Circular Pool Volume
Radius = diameter ÷ 2. Measure the pool straight across at the widest point to get the diameter, then halve that number to get the radius.
"Squared" means multiplying the radius by itself. If the radius is 9 ft, then radius² = 9 × 9 = 81 sq ft.
An 18 ft diameter pool (radius = 9 ft) at 4 ft average depth:
This circular pool pi formula applies equally to inground circular pools and round above-ground pools. For step-by-step fields, use the circular pool volume calculator.
Kidney and Irregular Pool Shapes
A kidney pool: A = 12 ft, B = 6 ft (A + B = 18 ft), 25 ft long, 5 ft average depth:
For complex freeform and lagoon shapes, divide the pool into simpler sections — rectangles and circles. Calculate each section's volume independently, then add the volumes together. For dedicated input fields, see the kidney pool volume calculator.
Pool Volume and Chemical Dosing (Parts Per Million)
Parts per million (ppm) is the concentration of a substance dissolved in water. Three parts of chlorine per one million parts of water = 3 ppm. Pool chemical labels express dosing targets in ppm.
Accurate pool volume matters because chemical dosing is calculated per gallon or litre of water. Overestimating pool volume by 33% leads directly to underdosing — water stays unsafe. Underestimating leads to overdosing, which causes skin and eye irritation.
Reference Figures for Pool Water Calculations
| Measurement | Value |
|---|---|
| 1 cubic foot of water | 7.48 US gallons / 28.3 litres |
| 1 cubic foot of water | 62.4 lbs / 28.3 kg |
| 1 US gallon of water | 8.33 lbs / 3.78 kg |
| 1 ppm | 8.3 lbs of chemical per million gallons |
1 gallon of liquid chlorine ≠ 1 ppm of chlorine in your pool volume, because chlorine is denser than water and varies by concentration percentage. Always follow the product label's dosing instructions based on your pool's exact volume in gallons.
What Is the Average Swimming Pool Volume?
The average residential swimming pool holds between 15,000 and 20,000 US gallons (57,000–76,000 litres). Knowing this range helps you sanity-check your calculator result — if your figure is significantly different, you may have entered dimensions incorrectly or used wall height instead of actual water depth.
Average volume also varies by shape. Round above-ground pools with a 12–18 ft diameter typically fall in the 2,500–7,600 gallon range — well below the average inground rectangular pool. For a deeper breakdown, see the average pool volume guide.
Common Pool Sizes — Quick Reference
Check your pool volume against these common sizes to ensure your calculations are in the right ballpark. These figures use an average depth of 5 feet for in-ground pools and standard wall heights for above-ground models.
For a complete breakdown of any specific dimension, use our pool volume by size reference guide.
| Size | Shape | Depth | US Gallons | Litres |
|---|---|---|---|---|
| 12 ft | Round | 48 in (4 ft) | ~2,500 | ~9,460 |
| 15 ft | Round | 52 in (4.33 ft) | ~7,630 | ~28,880 |
| 18 ft | Round | 54 in (4.5 ft) | ~15,270 | ~57,820 |
| 12 x 24 ft | Rectangular | 3.5 to 6.5 ft (Avg 5 ft) | ~10,800 | ~40,880 |
| 16 x 32 ft | Rectangular | 3.5 to 8.5 ft (Avg 6 ft) | ~23,760 | ~89,940 |
| 20 x 40 ft | Rectangular | ~33,000 | ~124,920 |
Pool Volume in Litres (Metric)
For regions using the metric system, pool volume is measured in litres (L) or cubic metres (m³). One cubic metre of water is exactly 1,000 litres. To convert your US gallon results to litres, multiply by 3.785. For a more detailed conversion table, visit our pool volume in litres guide.
Above-Ground Pool Volume
Yes — this calculator works for both above-ground and in-ground pools. Above-ground pools typically have a uniform water depth, which simplifies the capacity calculation: there is no shallow or deep end to average. Most above-ground pools are round or oval — select the correct shape in the calculator before entering dimensions.
Enter the actual water depth, not the pool wall height. Above-ground pools are rarely filled completely to the top of the wall, so using wall height overstates volume and causes incorrect chemical dosing. For a dedicated input form, use the above-ground pool volume calculator.
Olympic Swimming Pool Volume
The average backyard pool holds roughly 1/33 to 1/44 of an Olympic pool's total volume. A 15,000-gallon backyard pool would need to be filled roughly 44 times to match a single Olympic pool. For the full breakdown of Olympic swimming pool volume in all units, see the dedicated reference page.
Frequently Asked Questions
How do you calculate pool volume?
Pool volume is calculated by multiplying the pool's surface area by its average water depth to get cubic feet, then multiplying by 7.5 to convert to US gallons. For a rectangular pool: Length × Width × Average Depth × 7.5 = gallons. For circular pools, replace the surface area step with 3.14 × radius² × depth × 7.5. The pool volume calculator above returns results in gallons, litres, or cubic feet automatically — no manual calculation required.
What is the average volume of a swimming pool?
The average residential swimming pool holds between 15,000 and 20,000 US gallons (57,000–76,000 litres). Smaller above-ground pools typically hold between 5,000 and 10,000 gallons, while large inground pools can exceed 30,000 gallons (113,500 litres). The exact volume depends on the pool's shape, length, width, and depth — use the calculator above to get a precise figure for any pool size.
What is the volume of an Olympic swimming pool?
An Olympic swimming pool measures 50 metres long × 25 metres wide × 2 metres deep, giving a total volume of 2,500 cubic metres — equal to 2,500,000 litres or approximately 660,430 US gallons. For comparison, the average backyard pool holds only about 1/33 to 1/44 of that total volume, meaning it would take more than 33 average pools to fill a single Olympic pool.
Can I calculate pool volume in litres?
Yes — this calculator supports both US gallons and litres. Select your preferred unit before calculating to get results directly in litres. To convert manually, multiply any gallon result by 3.785 to get litres. Litres are the standard measurement for pool chemical dosing in Australia, the UK, and most of Europe, so an accurate litre volume is important for safe and correct pool maintenance.
Can I use this calculator for above-ground pools?
Yes. This calculator works for both above-ground and inground pools. Above-ground pools typically have a uniform water depth, which makes the calculation straightforward — enter the diameter (for round pools) or length and width (for oval pools) and the actual water depth. Do not use the wall height — measure only to the actual water level, because above-ground pools are rarely filled completely to the top of the wall.
Why does pool volume affect chemical dosing?
Pool chemical dosing — chlorine, pH adjusters, algaecide — is calculated per gallon or litre of water in the pool. An incorrect volume figure leads directly to incorrect chemical amounts. Overestimating pool volume by 33% results in underdosing, leaving the water unsafe. Underestimating results in overdosing, which causes skin and eye irritation. Parts per million (ppm) targets only make sense when the pool volume figure is accurate.
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