How do you calculate pool evaporation loss?

Multiply the water surface area by the daily evaporation depth in inches, by 0.623 gallons per square foot-inch, and by an exposure factor. For 512 ft2 at 0.25 in/day, that is about 79.7 gallons per day.

What is the 0.623 factor?

It is the volume conversion: one square foot of surface losing one inch of depth equals 0.623 gallons. It turns surface area times depth into gallons.

How much water does a pool lose to evaporation per day?

For a modest 512 square foot pool losing a quarter inch a day, roughly 80 gallons. Larger pools and hot, windy, dry conditions push this much higher.

How do I find the daily evaporation depth?

Use a local weather-based estimate or run a bucket test: float a bucket of pool water, mark both levels, and after 24 hours the drop in the pool relative to the bucket is your evaporation depth.

Does a pool cover reduce evaporation?

Yes, dramatically. A cover can cut evaporation by 50 to 95 percent, which you model here by lowering the exposure adjustment factor well below 1.

Evaporation loss vs make-up water rate?

Evaporation is only the surface vapor loss. Make-up water rate includes evaporation plus backwash, splash-out, and leaks, so make-up is always the larger of the two.

Pool, Spa & Water Treatment Chemistry calculator

Pool Evaporation Water Loss Calculator

Evaporation water loss estimates how many gallons per day a pool loses purely to water vaporizing from its surface. Pool operators and energy managers use it to separate normal surface loss from leaks, splash-out, and backwash, and to justify the payback on a pool cover. It is driven by surface area and the daily evaporation depth, which rises with heat, wind, low humidity, and warm water. Knowing the evaporation-only number lets you interpret the total make-up water rate correctly instead of blaming a leak for what the weather caused.

What this calculator does

Estimate evaporation loss from surface area, evaporation depth, and gallon conversion.
Use it to separate normal evaporation from possible leaks or to plan make-up water.
It computes the gallons per day lost to surface evaporation from a pool's water surface, adjusted for cover, wind, and humidity.

Formula used

Evaporation loss = surface area x evaporation depth x 0.623 x exposure adjustment

Inputs explained

Water surface area: Use water surface area, not deck area.
Daily evaporation depth: Use local weather estimate or bucket test result.
Gallons per square foot-inch: Use 0.623 gallons per square foot-inch.
Exposure adjustment factor: Adjust for cover use, wind, humidity, or indoor ventilation.

How to use the result

Use it when diagnosing high make-up water use or evaluating the water and heat savings of installing a pool cover.
Evaporation depth is highly weather-dependent, so a single assumed value can be off by more than double between a calm humid night and a hot windy afternoon.

Current U.S. benchmarks

Global copper trades at $13,552 per tonne (IMF via FRED, Jun 2026), up 37.8% in a year, and U.S. industrial electricity averages 8.66 cents per kWh. Both feed electrified-hardware unit economics.

Common questions

How do you calculate pool evaporation loss? Multiply the water surface area by the daily evaporation depth in inches, by 0.623 gallons per square foot-inch, and by an exposure factor. For 512 ft2 at 0.25 in/day, that is about 79.7 gallons per day.
What is the 0.623 factor? It is the volume conversion: one square foot of surface losing one inch of depth equals 0.623 gallons. It turns surface area times depth into gallons.
How much water does a pool lose to evaporation per day? For a modest 512 square foot pool losing a quarter inch a day, roughly 80 gallons. Larger pools and hot, windy, dry conditions push this much higher.
How do I find the daily evaporation depth? Use a local weather-based estimate or run a bucket test: float a bucket of pool water, mark both levels, and after 24 hours the drop in the pool relative to the bucket is your evaporation depth.
Does a pool cover reduce evaporation? Yes, dramatically. A cover can cut evaporation by 50 to 95 percent, which you model here by lowering the exposure adjustment factor well below 1.

Last reviewed 2026-05-12.