Pool Volume Calculator - Gallons, Litres & Average Depth
Pool gallons use surface shape and average depth. Rectangle uses length times width times depth times 7.48; round and oval pools use the common 5.9 factor.
Change any value and the results, formula, and diagram update immediately. Use the same unit system throughout one estimate.
Pool Gallons Quick Reference
Approximate volumes for common residential pool sizes. Use this for chemical dosing planning; the calculator handles your exact shape and depth.
| Pool size and shape | Average depth | US gallons | Imperial gallons | Litres |
|---|---|---|---|---|
| 12 x 24 ft rectangular | 5 ft | ~10,800 | ~9,000 | ~41,000 |
| 14 x 28 ft rectangular | 5 ft | ~14,700 | ~12,250 | ~55,600 |
| 16 x 32 ft rectangular | 5 ft | ~19,200 | ~16,000 | ~72,700 |
| 18 x 36 ft rectangular | 5.5 ft | ~26,700 | ~22,250 | ~101,000 |
| 24 ft round above-ground | 4 ft | ~13,500 | ~11,250 | ~51,100 |
| 27 ft round above-ground | 4 ft | ~17,200 | ~14,300 | ~65,100 |
| 15 x 30 oval above-ground | 4 ft | ~10,600 | ~8,800 | ~40,100 |
Conversion: 1 US gallon = 3.785 litres = 0.832 imperial gallons. 1 cubic foot of water = 7.48 US gallons = 28.3 litres.
The Pool Volume Formulas
Three formulas cover almost every residential pool:
- Rectangle: Gallons = Length x Width x Average depth x 7.48 (all in feet). Or m³ = L x W x D in metres, then x 1000 for litres.
- Round / Circular: Gallons = Diameter² x Average depth x 5.9. The 5.9 factor combines pi/4 with 7.48.
- Oval / Kidney: Gallons = Length x Width x Average depth x 5.9. Same factor as round; ovals approximate as elongated circles.
Average depth = (shallow + deep) / 2 for sloped-bottom pools. For a constant-depth pool, just use the depth.
Why Inside Water Dimensions, Not Shell Outside
Concrete pools have 6-10 in thick walls; vinyl liner pools have 4-8 in. Above-ground pools have steel walls 6-10 mm thick. Using outside dimensions overstates gallons by 5-15% on small pools and matters less on big ones.
- Measure at the waterline, not the top of the wall.
- Length and width: inside surface to inside surface.
- Depth: from the pool floor to the normal water level (about 4-6 in below the coping).
Chemicals - Dosing By Gallons
Pool chemical labels are dosed in ounces per 10,000 gallons or grams per 10 m³. Wrong volume means wrong chemistry.
| Chemical | Target level | Typical dose for 10,000 US gal |
|---|---|---|
| Free chlorine | 1-3 ppm | ~10-15 oz liquid chlorine (12.5%) |
| pH increaser (soda ash) | 7.4-7.6 | ~6 oz to raise pH 0.2 |
| pH decreaser (muriatic acid) | 7.4-7.6 | ~16 fl oz to lower pH 0.2 |
| Alkalinity (sodium bicarb) | 80-120 ppm | ~24 oz to raise 10 ppm |
| Calcium hardness | 200-400 ppm | ~14 oz calcium chloride for 10 ppm |
| Stabiliser (cyanuric acid) | 30-50 ppm | ~20 oz for 25 ppm rise |
| Shock (calcium hypochlorite 65%) | 10x current chlorine | ~1 lb to raise FC 10 ppm |
Always add chemicals to water, not water to chemicals. Run the pump while dosing. Wait 4 hours and re-test before adding more.
Filling a New Pool
- Garden hose: 5-12 gallons per minute typical. 20,000 gallon pool = 28-67 hours. Most communities ask you not to drain heaters and not to fill 10,000+ gallon pools at peak demand.
- Water truck delivery: 5,000-6,000 gallons per truck. Faster, cheaper than hose for big pools. Around $200-400 per delivery in the US.
- Cost from utility: $30-100 to fill a typical 15,000 gallon pool. Some jurisdictions waive sewer charges for pool fills - ask before filling.
- Hot tubs: use a hose; 400-800 gallons takes 1-2 hours.
Cost Estimates Around The World
2026 prices for residential pool installation and operating costs.
| Region | Above-ground (24 ft round) | Inground vinyl (16x32) | Inground concrete (16x32) | Annual operating |
|---|---|---|---|---|
| United States (USD) | $1,500-5,000 installed | $30,000-50,000 | $45,000-80,000+ | $1,500-3,500 |
| Canada (CAD) | C$2,500-7,000 | C$40,000-65,000 | C$60,000-110,000 | C$2,000-4,500 |
| United Kingdom (GBP) | £1,500-5,000 (less common) | £25,000-45,000 | £40,000-80,000 | £1,500-3,500 |
| Eurozone (EUR) | €2,000-7,000 | €30,000-55,000 | €50,000-100,000 | €1,800-4,000 |
| Australia (AUD) | A$3,500-9,000 | A$50,000-80,000 (fibreglass) | A$70,000-130,000 | A$2,500-5,500 |
| India (INR) | ₹150,000-450,000 (FRP shell) | ₹800,000-2,000,000 | ₹1,500,000-4,000,000+ | ₹80,000-200,000 |
| Mexico (MXN) | MX$40,000-150,000 | MX$400,000-700,000 | MX$600,000-1,200,000 | MX$30,000-80,000 |
| Philippines (PHP) | PHP 80,000-250,000 | PHP 800,000-1,800,000 | PHP 1,500,000-3,500,000 | PHP 60,000-150,000 |
Brand reference: US - Intex (above-ground), Anthony & Sylvan, Pinch A Penny; UK - Bestway, Intex; India - Reliable Aqua, Pentair, Hayward; Australia - Compass Pools, Narellan Pools.
Common Mistakes
- Using shell wall height instead of normal water level for depth.
- Using one corner depth on a sloped pool instead of average.
- Outside-of-wall length instead of inside water dimension.
- Mistaking imperial gallons (UK / India) for US gallons - they differ by 20%.
- Ignoring built-in seats and benches that reduce real volume by 5-10%.
- Confusing freshwater pool gallons with saltwater pool gallons (same volume, different chemistry).
- Filling pools without checking utility cap or sewer rebate eligibility.
- Using outdoor pool dosing for an indoor pool (different evaporation, different chlorine demand).
Pool Volume Calculator FAQ
How many gallons in a 16 x 32 ft pool?
With average depth 5 ft: 16 x 32 x 5 x 7.48 = 19,148 gallons (about 72,500 litres). Round and oval pools of similar size hold less - same formula but with a 5.9 factor instead of 7.48.
How do I calculate the volume of a round pool?
Diameter (ft) squared, times average depth (ft), times 5.9 = gallons. For a 24 ft round, 4 ft deep: 24 x 24 x 4 x 5.9 = 13,594 gallons (about 51,500 litres).
How do I find average depth on a sloped pool?
Add shallow-end depth + deep-end depth, divide by 2. A pool 3 ft shallow and 8 ft deep has average 5.5 ft. For complex shapes with multiple slopes, measure several depths and average them.
How many litres per US gallon?
3.785 litres per US gallon. So 20,000 US gallons = 75,700 litres. UK / Imperial gallons are different: 1 imp gal = 4.546 litres = 1.2 US gal.
How long to fill a pool with a garden hose?
Typical garden hose flow is 5-12 gallons per minute. A 20,000 gallon pool takes 28-67 hours - usually 2-3 days non-stop. Water trucks deliver 5,000-6,000 gallons in one trip.
How much chlorine for my pool?
For 10,000 gallons, 10-15 ounces of 12.5% liquid chlorine raises free chlorine by 1 ppm. Daily dose depends on bather load, sun exposure, and CYA level. Test daily during swim season.
What is the ideal pool pH?
7.4-7.6 is the target range. Below 7.2 corrodes metal and irritates skin; above 7.8 causes cloudiness and reduces chlorine effectiveness. Test and adjust 2-3 times a week.
Why is manufacturer pool volume different from my calculation?
Pool manufacturers account for benches, seats, rounded corners, fill line below coping, and plumbing displacement. Their gallons may be 5-15% lower than a simple geometric calculation.
How often should pool water be changed?
Outdoor concrete pools: every 5-7 years complete drain. Vinyl liner pools: every 7-10 years when the liner is replaced. Daily replenishment is just topping up from evaporation - about 1/4 to 1/2 inch per day in summer.
What is the cost to fill a swimming pool?
US: $30-100 from utility for 15,000 gallons (rates vary by city). Water truck: $200-400 per 5,000 gallons. UK: £30-80 metered. India: typically free from municipal supply but coordinated with society tanker delivery.
Related Construction Calculators
For smaller spas, use the Hot Tub Gallons Calculator. For non-pool water tanks, see the Water Tank Volume Calculator. For pool surround paving, the Paver Calculator. More tools live on the Construction Calculators hub.
Sources
- Pool & Hot Tub Alliance (PHTA) standards and resources
- CDC Healthy Swimming - chemistry and safety
- ANSI/APSP/ICC-7 Standard for Suction Entrapment Avoidance
- Pool & Spa News water chemistry references
- NIST Handbook 44 unit conversion tables
This calculator is for planning and ordering conversations. Local code, project drawings, engineered design, and manufacturer instructions control the final work.