Pool Calculator
Pick your pool shape and enter dimensions to get the surface area, volume, and gallons for sizing chemicals, heaters, and pumps.
What your result means
Gallons drives chemical dosing; surface area drives heat loss, solar gain, and cover sizing. Rough rules: a heater needs about 1 BTU/hour per gallon to raise the water a degree, and a pump should turn the whole pool over in 8 to 10 hours. Solar blankets are sold by the square foot of surface.
How to use this calculator
- Pick shape, enter dimensions.
- Read surface area, volume, and gallons.
- Surface area for chemicals, gallons for dosing.
- Helps size heaters, pumps, and filters.
- Surface area also for cover/solar blanket sizing.
The formula
Surface area is the rectangle, circle, or ellipse area. Multiply by average depth for cubic feet, then by 7.48 for gallons.
Worked example
Say you've got a 30 by 15 ft rectangular pool at 5 ft average depth. That's 450 sq ft of surface, 2,250 cubic feet, and 16,831 gallons.
Pool sizing rules of thumb
| Job | Rule |
|---|---|
| Heater | ~1 BTU/hr per gallon per degree |
| Pump turnover | whole pool in 8 – 10 hrs |
| Solar blanket | by surface area (sq ft) |
| Chemicals | by gallons |
Tips & gotchas
- Use surface area for solar covers and heat-loss math.
- Use gallons for chemical dosing.
- Heater sizing is about 1 BTU/hour per gallon to raise the water a degree.
- Size the pump to turn the pool over in 8 to 10 hours.
- Solar blankets are sold by the square foot.
Frequently asked questions
What is pool surface area?
The water surface in square feet, used for solar covers and heat-loss math.
Why does surface area matter?
Heat is lost and gained through the surface, while chemicals dose by gallons.
How big a heater do I need?
About 1 BTU/hr per gallon per degree. A 20,000 gallon pool needs roughly 20,000 BTU/hr per degree.
What size pump for my pool?
One that turns the pool over in 8 to 10 hours. 20,000 gallons over 10 hours is about 33 GPM.
Do round pools have less surface area?
Yes, for the same overall dimensions, since there are no corners.
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Estimates only — see our full disclaimer.