About Pool Volume Calculator (Gallons & Liters)
The pool volume calculator answers "how many gallons is my pool?" for the four common plan shapes — rectangular, round, oval, and kidney — using the same multiplier formulas the pool industry publishes (Pentair engineering data and the Pool & Hot Tub Alliance's consumer guidance). Pick the shape, enter the dimensions measured at the water line, and give the depths: either the shallow-end and deep-end pair, which the tool averages, or one constant depth for a flat-bottom pool.
Gallons is the headline number because everything downstream keys off it — chlorine and shock dosing, pump turnover, filter and heater sizing, and what the first fill will cost. The tool also converts to liters (× 3.78541), reports the water weight at 8.34 lb per gallon, and, when you enter your water rate in dollars per 1,000 gallons from a utility bill, prices the first fill.
How It Works
- Pick the pool shape. Each shape keeps its own dimension fields, so switching shapes never carries a value across.
- Measure at the water line, not the coping or the outside of the wall — the formulas estimate water, not shell. For an oval, use the full length and full width; for a kidney, the overall length and the width across each lobe.
- Enter the shallow-end and deep-end depths and the tool uses their average, or flip the constant-depth toggle for a flat-bottom (above-ground) pool. The average works because a typical pool floor slopes roughly evenly from end to end.
- Read the gallons headline, with liters and the water weight below it. Water weight matters for decks, above-ground pool bases, and anything structural: 21,000 gallons is about 88 US tons.
- Optionally enter your water rate in $ per 1,000 gallons (from your utility bill) to price the first fill.
Worked Example
Start with the first row of the table below: a 32 × 16 ft in-ground rectangle sloping from 3 ft at the shallow end to 8 ft at the deep end. Average depth = (3 + 8) / 2 = 5.5 ft. Gallons = 32 × 16 × 5.5 × 7.5 = 21,120. Liters = 21,120 × 3.78541 ≈ 79,948. Water weight = 21,120 × 8.34 ≈ 176,141 lb — about 88 US tons. At a water rate of $4 per 1,000 gallons, the first fill costs 21.12 × $4 = $84.48.
How many gallons is my pool?
Chlorine doses, pump turnover, heater sizing, the first-fill bill — every one of them keys off the gallons below. Dimensions are taken at the water line: rectangles and kidneys use the industry 7.5 gal/ft³ multiplier, rounds and full-axis ovals the 5.9 factor — π/4 × 7.5, the ellipse’s share of its bounding rectangle. The in-ground rows average their shallow and deep ends; the above-ground rows use one flat-bottom depth as-is. Liters convert at 3.78541 per gallon and the weight column at 8.34 lb per gallon — worth reading before parking 57 tons of water next to a deck.
| Pool | Average depth (ft) | US gallons | Liters | Water weight (lb) |
|---|---|---|---|---|
| 16 × 32 ft rectangle, 3 ft shallow to 8 ft deep | 5.50 | 21,120 | 79,948 | 176,141 |
| 15 × 30 ft rectangle, 3 ft shallow to 6 ft deep | 4.50 | 15,188 | 57,491 | 126,664 |
| 24 ft round above-ground, 4 ft of water (flat bottom) | 4.00 | 13,594 | 51,457 | 113,371 |
| 15 ft round above-ground, 4 ft of water | 4.00 | 5,310 | 20,101 | 44,285 |
| 15 × 30 ft oval above-ground, 4 ft of water | 4.00 | 10,620 | 40,201 | 88,571 |
| 32 ft kidney (lobes 16 and 10 ft), 3 ft shallow to 8 ft deep | 5.50 | 15,444 | 58,462 | 128,803 |
Formulas
- Average depth
AD = (D_shallow + D_deep) / 2- Rectangular pool
gallons = L × W × AD × 7.5- Round pool
gallons = Dia × Dia × AD × 5.9- Oval pool
gallons = L × W × AD × 5.9- Kidney pool
gallons = 0.45 × (A + B) × L × AD × 7.5- Conversions
liters = gallons × 3.78541; weight = gallons × 8.34 lb; fill cost = gallons / 1000 × rate
Standards & References
- Pentair Pool Product Catalog 2025–2026, Engineering Data — "Estimating Total Gallons in a Pool or Spa" (p. 526)
- Pool & Hot Tub Alliance (PHTA) swimmingpool.com pool-volume guidance — 0.45 × (A+B) kidney formula
- 1 ft³ = 7.48052 US gallons exactly; the industry rounds to 7.5
Frequently Asked Questions
How many gallons is a 32 × 16 ft pool?
With a 3 ft shallow end and an 8 ft deep end, the average depth is 5.5 ft and the volume is 32 × 16 × 5.5 × 7.5 = 21,120 gallons — about 80,000 liters, weighing roughly 176,000 lb. A flat 4 ft version of the same pool holds 32 × 16 × 4 × 7.5 = 15,360 gallons.
Why does the formula use 7.5 gallons per cubic foot instead of 7.48?
A cubic foot holds exactly 7.48052 US gallons, but every published pool formula — Pentair's engineering data, PHTA guidance, pool-store charts — rounds to 7.5. The rounding runs about 0.3% high, which is far smaller than the error in measuring a real pool at the water line, and chemical dose ranges absorb it easily. The 5.9 round/oval factor carries the same rounding: π/4 × 7.5 = 5.89.
Why does averaging the shallow and deep depths work?
Most in-ground pools slope roughly evenly from the shallow end to the deep end, so the cross-section is close to a trapezoid — and the volume of that prism is exactly the surface area times the average of the two end depths. If your pool has a distinct shallow shelf, a steep drop-off, or a diving well, split it into sections, compute each with its own average depth, and add the gallons.
Is the oval formula exact?
The 5.9 factor treats the oval as a true ellipse (π/4 of the bounding rectangle, × 7.5 gal/ft³). Many above-ground "ovals" are really rectangles with rounded ends and hold more water than an ellipse — Pentair's engineering table prints 6.7 gal per ft of L × W × depth for those straighter-sided shapes. If your oval has long straight side walls, the truth lies between the two; the ellipse figure here is the conservative one most pool calculators publish.
How many gallons is a 24-foot round pool?
With 4 ft of water, a 24-ft round holds 24 × 24 × 4 × 5.9 ≈ 13,594 gallons. The diameter is squared, so size cuts both ways fast: a 15-ft round at the same 4 ft holds just 5,310 gallons, and every extra half-foot of water in the 24-footer adds about 1,700 gallons. Measure the actual water depth, not the wall height — above-ground pools are never filled to the rim.
How many gallons is a 15 × 30 oval above-ground pool?
At 4 ft of water, 15 × 30 × 4 × 5.9 = 10,620 gallons by the ellipse formula. If your oval has long straight side walls — most buttressed above-ground ovals do — it holds more than a true ellipse, and Pentair's engineering table uses 6.7 instead of 5.9 for those shapes; the ellipse figure here is the conservative one. Either way, retest and fine-tune chemical doses after the first season of readings.
How much does pool water weigh?
A US gallon of water weighs 8.34 lb, so the weight column adds up quickly: the 24-ft round in the table carries about 113,371 lb — 57 US tons — and the 21,120-gallon rectangle about 176,141 lb. That mass is why above-ground pools need a prepared, level base and why a deck must carry itself rather than lean on a pool wall — check the weight line before planning anything structural around the water.
How much does it cost to fill a pool?
Find the water rate on your utility bill — US residential rates commonly run about $2 to $10 per 1,000 gallons — and enter it in the tool. A 21,120-gallon pool at $4 per 1,000 gallons costs 21.12 × $4 ≈ $84 in water for the first fill, before any sewer charge your utility may or may not apply to pool fills (many will waive it on request).
What do I do with the gallons number?
Nearly every pool decision keys off volume: chlorine, shock, and balancer doses are stated per 10,000 gallons; the pump and filter are sized so the whole volume turns over in roughly 8–12 hours (see the pump sizing calculator for head-loss and duty-point selection); and heaters are sized from gallons and the temperature rise. Keep the number with your pool records — you will use it every season.