DIY Cost Tools
Pool Evaporation Calculator
Estimate water loss and refill cost from pool surface area, observed daily evaporation, number of days and water price.
How to use this calculator
- Replace every example value with your own measurements, label values or planning assumptions.
- Keep each value in the unit printed beside its field.
- Select Calculate, then compare the result with the formula and limitations below.
Formula and method
Gallons lost = surface square feet × daily inches ÷ 12 × 7.48052 × days. Cost = gallons ÷ 1,000 × water price.
Results are hidden whenever an input changes or validation fails, so an older answer cannot be mistaken for the current calculation.
Worked example
Pool surface area = 500 sq ft; Average daily evaporation = 0.25 in/day; Number of days = 7 days; Water price = 5 $/1,000 gal. The calculator returns Estimated water loss = 545 gal; Estimated refill cost = 2.73; Depth lost = 1.75 in.
The worked example uses the same default values displayed in the calculator.
Limitations and safety
Frequently asked questions
What should I enter first?
Start with measurements or rates from the project, product label, service quote or equipment specification. Replace every example value before relying on the estimate.
Why can the real result differ?
Wind, temperature, humidity, covers, splashing, backwashing and leaks affect water loss. A persistent drop greater than measured evaporation may indicate a leak that needs inspection.
Does the calculator round purchases up?
Only outputs labeled as whole packages, vents, heaters, pails or similar counts are rounded up. Keep extra precision for planning and follow supplier packaging.
Review notes and reference
Reviewed October 5, 2026. The formula was independently checked against the displayed default example, and the calculator was tested for valid defaults, empty input, invalid formats, range boundaries and recovery. Reference: EPA WaterSense. Explanations and examples are original.