PoolOwl

Pool size

Pool Surface Area Calculator

Get your pool's water surface area in square feet, the number heater sizing and cover sizes are based on.

What you'll need (2)
  • A tape measure
  • Your pool's shape
Units
Pool shapePick the closest match. Freeform lets you enter a measured area.
Surface measurements

Measure the water surface, inside wall to inside wall, not the deck or coping.

The longest straight measurement. Example: 32.
Measured across the middle. Example: 16.

Your result

Calculated

Your result will appear here

Enter your pool's measurements to see its surface area.

What surface area is used for

Surface area is the area of the water you can see from above. It drives three things:

  • Heater sizing. Heat escapes mainly from the surface, so the US Department of Energy’s rule of thumb for outdoor pool heaters starts from square feet. Our heat pump sizing calculator uses this number.
  • Covers. Solar and winter covers are sold by pool dimensions, and the area tells you how much water a cover is protecting.
  • Evaporation and refill. One inch of water lost over your surface area is the volume you’ll need to top up.

Formulas

Shape Surface area
Rectangle length × width
Round 3.1416 × (diameter ÷ 2)²
Oval (ellipse) 3.1416 × (length ÷ 2) × (width ÷ 2)
Kidney 0.45 × (A + B) × length (an industry approximation)

For an irregular pool, divide it into simple shapes on paper, work out each one and add them together.

Assumptions and limitations

  • Measures the water surface only. Include steps, a sun shelf or a connected spa only if you measure them in.
  • Ovals are treated as ellipses; ovals with straight sides have slightly more area.
  • Kidney shapes use the 0.45 × (A + B) × length approximation.

Common questions

Why does heater sizing use surface area instead of gallons?

Most of a pool's heat escapes from the water surface through evaporation, radiation and wind. That's why the US Department of Energy's sizing rule multiplies surface area, not volume, by the temperature difference.

Do I include the steps or a spa in the surface area?

Include any open water connected to the pool, including a sun shelf. If a spa spills into the pool but is heated separately, measure it on its own.

Sources and methodology references

  1. NIST Special Publication 811: unit conversion factors, National Institute of Standards and Technology1 square meter = 10.7639 square feet.

Published October 2, 2026. Results are calculated directly from your inputs. See how our calculators work.

Spotted a wrong result or an outdated source? Report a problem with this calculator.

Related tools

Related guides