Pool Volume Calculator

How Pool Volume Is Calculated

For a rectangular pool, volume equals length × width × average depth × 7.48 gallons per cubic foot. For round pools, use π × (diameter/2)² × average depth × 7.48. Oval pools use (π/4) × length × width × depth × 7.48. Kidney-shaped pools use 0.85 × length × width × depth × 7.48, because the curves lose about 15 percent of the bounding rectangle. Always use average depth for pools with sloped bottoms, not maximum depth.

Measuring Average Depth

Most residential pools are deeper at one end than the other. For a simple sloped bottom, average depth is (shallow end + deep end) / 2. For a pool with a flat shallow area, then a slope, then a flat deep area, the math is: (shallow_area × shallow_depth + slope_area × average_slope_depth + deep_area × deep_depth) / total_area. For most purposes, the (shallow + deep) / 2 shortcut is within 10 percent of the true volume.

Why You Need Your Pool's Volume

Chemical dosing is the main reason. Every chlorine, algaecide, shock, pH balancer, and stabilizer product on the market lists dosing in ounces or pounds per 10,000 gallons. Get your volume wrong and you will either waste chemicals or fail to sanitize the pool. Volume also matters for heating — each 1°F rise in a 20,000 gallon pool requires about 167,000 BTU of heat input, which informs whether a 400,000 BTU gas heater or a 100,000 BTU heat pump is appropriate for your climate. Finally, volume tells you water cost for initial fill and refills after draining.

Typical Residential Pool Volumes

A 12 × 24 foot rectangular above-ground pool at 4 foot average depth holds 8,620 gallons. A 16 × 32 inground pool at 5 foot average holds 19,150 gallons. A 20 × 40 pool at 6 foot average holds 35,900 gallons. A 24 foot round above-ground at 4 foot depth holds about 13,600 gallons. Standard backyard inground pools are usually 15,000 to 30,000 gallons. Anything over 50,000 gallons is a commercial or large residential pool and usually warrants a larger pump, heater, and sanitation system.

Frequently Asked Questions

How many gallons per cubic foot of water?

7.48 US gallons, or about 28.3 liters.

Do I use average or max depth?

Average depth — always. Max depth overstates volume by 20 to 40 percent for most residential pools.

How long does it take to fill a pool?

At a typical 10 GPM garden hose flow, a 20,000 gallon pool takes about 33 hours. Truck delivery is faster and often cheaper for the initial fill.

Is my pool volume more or less after adding a hot tub?

If the hot tub is plumbed to the pool pump, add the hot tub volume to the total for chemical dosing.

How do I dose chlorine from volume?

Liquid chlorine (12.5%): ~11 oz per 10,000 gallons to raise free chlorine by 1 ppm.