Free pool evaporation calculator. Calculate how much water your pool loses daily based on temperature, humidity, wind, and pool size using ASHRAE methods.
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Pool evaporation is a natural process that can cause significant water loss. Our calculator uses the ASHRAE method to estimate how much water your pool loses based on water temperature, air conditions, wind, and pool activity. Understanding evaporation helps you plan water management and identify potential leaks.
Pool evaporation occurs when water molecules at the surface gain enough energy to escape into the air as vapor. The rate depends on the vapor pressure difference between the water surface and the surrounding air. Higher water temperatures, lower humidity, and wind all increase evaporation.
ASHRAE Evaporation Formula
Homeowners estimate water top-up needs and compare to actual usage.
Hotels and fitness centers plan water and heating budgets.
Justify pool cover investment by calculating water and energy savings.
Compare calculated evaporation to actual water loss to detect leaks.
Know how much water you need to add and plan for water costs.
Distinguish between normal evaporation and potential pool leaks.
Evaporation causes significant heat loss that affects heating costs.
A typical outdoor pool loses 1/8 to 1/4 inch (3-6mm) per day in moderate climates. This equals about 50-100 gallons daily for a standard 15×30 ft pool. Desert climates can see 1/2 inch or more daily.
Pool covers are the most effective solution, reducing evaporation by up to 95%. Liquid solar covers, windbreaks, and lowering water temperature also help. Keeping the pool out of direct wind reduces evaporation significantly.
Use the bucket test: Fill a bucket to match pool water level, place it on the pool step, and compare water loss after 24 hours. If the pool loses more than the bucket, you likely have a leak.
Yes. ASHRAE assigns each pool an activity factor by occupancy: about 0.5 for a quiet residential pool, 0.8 for a hotel pool, 1.0 for a busy public pool, and up to 1.5 for wave pools and water parks. A heavily used pool can evaporate 2–3× more than a still one because splashing and wet decks expose more water surface.