Pool Evaporation Calculator — Gallons and Refill Time
Use an evaporation-only daily depth from a documented local estimate, weather model or controlled benchmark, then convert that depth across the pool surface into gallons. The calculator can model a cover reduction, refill flow and local water rate, but unexplained observed level loss must be investigated separately.
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View all saved project estimatesWhat does the pool evaporation calculator calculate?
Enter an uncovered daily evaporation estimate, not unexplained pool level loss. The calculator converts that evaporation depth into gallons from surface dimensions and days, models your entered cover reduction, then estimates refill time and optional water cost. It does not predict local weather, identify leaks, or include splash-out and backwashing.
Pool evaporation depth to gallons, refill time and cost
Length, width, and shape factor estimate water-surface area. Converting the evaporation-only depth from inches to feet turns that area into cubic feet, and 7.48052 converts cubic feet to U.S. gallons. Days and the entered cover reduction model one explicit evaporation scenario; refill flow and the optional local rate estimate time and water-only cost.
How to measure for an accurate estimate
- Measure length and width across the operating waterline; use 100% for a rectangle or 78.54% for a true ellipse measured across full axes.
- Obtain an uncovered evaporation-only depth from a credible local weather model, documented study, or controlled same-condition benchmark rather than unexplained pool-level observations.
- Track rainfall, deliberate refilling, backwashing, splash-out, overflow and suspected leaks separately; a cover reduction must never be applied to those other losses.
- Measure refill flow by timing a known container at the actual outlet, and enter the applicable marginal water rate plus a cover-reduction value supported by the scenario.
Seven-day rectangular pool benchmark
A rectangular pool has a 30-by-15-foot water surface and uses a 100% shape factor. The owner enters a documented uncovered evaporation estimate of 0.25 inch per day for seven days, applies no cover reduction, and measures refill flow at 8 gallons per minute. Rainfall, backwashing, splash-out, overflow, automatic refill activity and unexplained loss are excluded entirely from that evaporation input.
The 450-square-foot surface converts the entered evaporation depth to about 70.13 gallons per day and 491 gallons over seven days. At 8 gallons per minute, replacing that modeled quantity would take approximately 61.4 minutes; cost remains blank until a local water rate is entered.Before you purchase material
- Use a properly fitted cover consistently when appropriate, following its manufacturer’s operation, maintenance, and safety instructions.
- Check autofill controls, overflow paths, pump schedules, water features, filter-cleaning practices, and logged rainfall before interpreting water-use changes.
- Compare water costs with the utility’s current marginal rate and any sewer treatment charges or drought restrictions that actually apply.
- If unexplained water loss continues, use qualified pool service guidance rather than treating this geometry conversion as a leak test or repair recommendation.
Common questions
Does this pool evaporation calculator detect a leak?
No. It converts an evaporation-only planning depth into volume. Rain, splash-out, backwashing, overflow, autofill operation, measurement error and leaks can all change observed level but do not belong in that input. Persistent unexplained loss needs an appropriate inspection or test.
What daily pool evaporation rate should I enter?
Use an uncovered evaporation-only value from a credible local model, documented study or controlled benchmark. The calculator does not supply a normal rate because air temperature, water temperature, humidity, wind, exposure, heating and water features vary substantially by pool and day.
How does the pool cover reduction input work?
It reduces only the entered uncovered evaporation baseline by the percentage you provide. It never reduces leakage, splash-out, backwashing or overflow. Use zero for no modeled reduction; actual savings depend on cover type, fit, surface coverage, operating schedule, weather and consistent use.
How do I measure the pool refill flow rate?
Fill a container of known gallon capacity from the actual outlet and time it in seconds. Gallons per minute equals container gallons multiplied by 60, divided by seconds. Repeat the measurement because pressure and simultaneous household water use can change the available flow.
Sources and reference standards
- U.S. EPA WaterSense — Pool Water EfficiencyFederal water-efficiency guidance discussing evaporation, pool covers, maintenance, and the need to manage other sources of pool water loss separately.
- National Institute of Standards and Technology — Volume Conversion FactorsFederal reference for U.S. customary volume units and conversion relationships used when area and depth become cubic feet.
Use this result in a complete project plan
Pool circulation planner
Pool circulation planning begins with credible water volume, but gallons divided by hours is only an average flow target. It cannot reveal pipe resistance, filter condition, required equipment flow, sanitation or pump horsepower. This guide connects volume, turnover, runtime, measured watts and operating cost while keeping hydraulics, electrical work, water treatment and local operating requirements with qualified sources and professionals.
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