Pool Evaporation Calculator

This estimates how fast a swimming pool loses water to evaporation, using the Carrier equation in the form printed in the ASHRAE Handbook. Enter the surface area, the water and air temperatures, the relative humidity, the air speed over the water and the type of pool, and you get the rate in inches and gallons a day, the heat that evaporation carries out of the water and, if you add your water and gas prices, what that costs. The figure is only as good as the air speed you give it, and the equation is very sensitive to that number, so a sheltered pool and an exposed one at the same forecast wind are not the same pool. A cover is the one variable that dominates the answer.

Area Unit
Temperature Unit
Air Speed Unit
Water Price Per
Gas Price Per
The area of the water surface seen from above. A rectangle is length times width; for any other shape use the surface area, not the volume.
The air actually moving across the water, not the forecast wind. An indoor pool sits near 0.1 to 0.3 mph, which is 0.04 to 0.13 m/s; a fenced or screened garden pool near 0.5 to 1 mph, 0.2 to 0.45 m/s; an open exposed pool on a breezy day 2 to 5 mph, 0.9 to 2.2 m/s. Shelter matters more than the forecast does.
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