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
A 32 × 16 ft in-ground rectangle slopes 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.
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 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.