Pool Evaporation Rate Calculator

Plan top-ups and cover strategies by estimating how many liters evaporate from your pool each day. Combine surface area, water temperature, humidity, and wind to anticipate water usage, chemical balancing, and cover savings.

Multiply length by width for rectangular pools or use the Pool Volume calculator to approximate irregular shapes.
Measure water temperature in the morning before sun and pumps change conditions.
Use local weather data or a hygrometer near the pool surface.
Estimate breeze speed at water level; even 1 m/s of airflow boosts evaporation.

Educational information, not professional advice.

Examples

  • Family pool: 48 m² surface, 27 °C water, 55% humidity, 2.0 m/s wind ⇒ 5,781 L/day (≈ 120 mm/month).
  • Compact plunge pool: 32 m² surface, 22 °C water, 45% humidity, 1.2 m/s wind ⇒ 3,121 L/day (≈ 3.1 mm/day).
  • Indoor pool: 60 m² surface, 29 °C water, 60% humidity, 0.5 m/s wind ⇒ 4,005 L/day before dehumidification.

FAQ

Does this include splash-out or backwash losses?

No, it only models evaporation. Add those volumes separately for a full water budget.

Can I use Fahrenheit and mph?

Convert them first using the Fahrenheit to Celsius and Feet per Second to MPH calculators.

Will a solar cover change the result?

A cover greatly reduces evaporation; rerun the calculation with a lower effective wind speed (often 0.2–0.5 m/s) to approximate the benefit.

How often should I remeasure conditions?

Check humidity, temperature, and wind weekly during swimming season—weather swings can double or halve evaporation rates.

Additional Information

  • Formula adapted from empirical ASHRAE evaporation correlations for outdoor pools under light wind conditions.
  • Installing a solar or thermal cover overnight can reduce evaporation by 50–70%; plug the reduced wind speed into this calculator to model the benefit.
  • Convert the result to gallons by dividing by 3.785, or to cubic metres by dividing by 1,000, if your supplier bills in those units.
  • Pair the output with the Water Efficiency Savings calculator to understand cost and sustainability impacts of refilling.
  • Track evaporation alongside chemical readings—top-ups dilute sanitizer and alkalinity, so adjust dosing schedules accordingly.

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