Pool Volume Calculator

What this pool volume calculator does

This calculator works out the water volume of your pool in US gallons, litres and cubic metres — the three units pool equipment, chemical doses and heater specs are quoted in. Pick the shape (rectangle, circle, or oval), type the dimensions in feet or metres, and the result updates instantly. Every dose chart you’ll see for the rest of your pool’s life is keyed off the gallon number this calculator gives you, so it’s worth getting right the first time and writing the answer on a small tag at the equipment pad.

How to use the pool volume calculator

1. Pick a shape. Rectangle is the default for in-ground pools; use Circular for stock-tank pools and round above-grounds; use Oval for classic above-ground frame pools.
2. Switch between feet and metres — the calculator handles both. Most US pool stores work in gallons; European installers want litres.
3. Enter the length and width (or diameter, for round pools). Measure inside the pool wall, not the deck.
4. Enter the shallow-end and deep-end depths. The calculator averages them automatically. For a constant-depth pool, use the same value in both fields.
5. Read the result. The headline gallon number is what you use for every chemical dose. Tap Copy summary to text it to your pool service or paste it into a chemical-dose spreadsheet.

How average depth works for sloped pools

Most in-ground pools and many above-grounds have a sloped floor — the floor drops gradually from a shallow end (often 3 ft) to a deep end (often 5–8 ft). The actual water volume the pool holds is set by the average depth, not the deep-end depth.

For a linear slope — the most common construction — the average is exactly the arithmetic mean of the two ends: (shallow + deep) ÷ 2. So a 3 / 6 ft sloped pool averages 4.5 ft. Use that 4.5 ft figure with length × width × depth × 7.48 to get gallons.

For pools with a flat bottom on each end and a sharp transition zone (the “spoon” or “hopper” design), the actual average is slightly higher than the linear average. You can get within 1 % by sketching the pool’s cross-section, computing the area, and multiplying by the average pool width. Most homeowners don’t bother — the linear average is accurate enough for chemistry.

Why pool volume matters

Volume drives every pool decision you’ll make for the next twenty years.

• Chlorine dosing. “10 fl oz of 12.5 % liquid chlorine raises a 10,000 gallon pool by 1 ppm” — every chlorine, shock, and stabiliser chart is quoted per gallons. Get volume wrong and you under-dose (algae) or over-dose (faded vinyl, irritated eyes).
• Salt-chlorinator targets. A salt-water generator wants 3,000–3,500 ppm salinity. Going from 0 to 3,200 ppm in a 20,000 gal pool takes ~530 lb of pool salt; in a 10,000 gal pool, half that. A bad gallon estimate means thirteen 40-lb bags of salt instead of six.
• Heater sizing. Raising the pool 1 °F per hour takes ~8 BTU per gallon. A 20,000 gal pool needs a 160,000 BTU heater for that rate; for a faster heat-up, oversize the heater.
• Pump and filter sizing. Turnover rate (the time to circulate every gallon once) drives pump GPM and filter area selection. Industry standard is one full turnover every 8 hours — meaning a 20,000 gal pool needs a pump moving ~42 GPM.

Daily evaporation rules of thumb

Once you know your gallons, you can predict daily losses:

• Hot, dry, sunny (Phoenix, Vegas, west Texas): ~¼ inch / day evaporation. About 1–2 % of total volume per week.
• Humid southern US (Houston, Orlando, Atlanta): ~⅛ inch / day. About ½–1 % per week.
• Temperate / coastal (LA, San Diego, North Carolina): ~⅛ inch / day in summer; almost zero in winter.

A pool cover cuts losses 50–95 %, depending on cover type. Anything more than ½ inch / day with a cover on, or 1 inch / day without, points to a leak. The bucket test (a bucket of water on the top step, water inside matched to pool level, compare drop after 24 hours) is the cheapest way to confirm.

Privacy

This calculator does its arithmetic in JavaScript on your device. There is no fetch call, no analytics on the dimensions you enter, no server-side logging. The page works the same way offline once loaded.