{"id":"pool-evaporation-calculator","name":"Pool Evaporation Calculator — Gallons and Refill Time","shortName":"Pool Evaporation","canonicalUrl":"https://calcurhome.com/calculators/pool-evaporation-calculator","catalogUrl":"https://calcurhome.com/api/calculators","category":{"id":"pools-spas","name":"Pools & spas","url":"https://calcurhome.com/calculators/category/pools-spas"},"language":"en-US","audience":"US homeowners, DIYers and home-project planners","primaryKeyword":"pool evaporation calculator","secondaryKeywords":["pool water loss calculator","pool evaporation gallons calculator","pool refill time calculator","pool cover water savings calculator","swimming pool level loss","inches of pool water to gallons"],"description":"Convert an uncovered pool-evaporation depth into gallons, model a cover reduction, and estimate refill time and water cost from local inputs.","directAnswer":"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.","inputs":[{"key":"length","label":"Water-surface length","unit":"ft","defaultValue":30,"min":0.1,"max":10000,"step":0.1,"help":"Measure across the waterline, not outside coping or walls."},{"key":"width","label":"Water-surface width","unit":"ft","defaultValue":15,"min":0.1,"max":10000,"step":0.1},{"key":"shapeFactor","label":"Surface shape factor","unit":"%","defaultValue":100,"min":1,"max":100,"step":0.01,"help":"Use 100% for a rectangle or 78.54% for a true ellipse measured across full axes."},{"key":"dailyLevelLoss","label":"Uncovered daily evaporation","unit":"in/day","defaultValue":0.25,"min":0,"max":24,"step":0.01,"help":"Enter an evaporation-only local estimate or controlled benchmark, not total unexplained water loss."},{"key":"days","label":"Planning period","unit":"days","defaultValue":7,"min":1,"max":3650,"step":1},{"key":"coverReduction","label":"Entered cover reduction","unit":"%","defaultValue":0,"min":0,"max":100,"step":1,"help":"Use a documented or scenario value; zero represents the entered uncovered benchmark."},{"key":"refillRate","label":"Measured refill flow","unit":"gal/min","defaultValue":8,"min":0.1,"max":100000,"step":0.1,"help":"Measure flow at the actual hose, valve, or fill outlet."},{"key":"waterRatePerThousandGallons","label":"Optional local water rate","unit":"$/1,000 gal","defaultValue":0,"min":0,"max":10000,"step":0.01,"help":"Use the applicable marginal water rate; add sewer or other charges separately when they apply."}],"formula":{"title":"Pool evaporation depth to gallons, refill time and cost","expression":"Gallons = length × width × shape factor × (daily uncovered evaporation in inches ÷ 12) × 7.48052 × days × (1 − cover reduction %). Refill minutes = gallons ÷ measured refill GPM. Water cost = gallons ÷ 1,000 × local water rate.","explanation":"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."},"measurementGuide":["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."],"buyingTips":["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."],"workedExample":{"title":"Seven-day rectangular pool benchmark","scenario":"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.","result":"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."},"commonQuestions":[{"question":"Does this pool evaporation calculator detect a leak?","answer":"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."},{"question":"What daily pool evaporation rate should I enter?","answer":"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."},{"question":"How does the pool cover reduction input work?","answer":"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."},{"question":"How do I measure the pool refill flow rate?","answer":"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":[{"name":"U.S. EPA WaterSense — Pool Water Efficiency","url":"https://www.epa.gov/watersense/pool-water-efficiency","note":"Federal water-efficiency guidance discussing evaporation, pool covers, maintenance, and the need to manage other sources of pool water loss separately."},{"name":"National Institute of Standards and Technology — Volume Conversion Factors","url":"https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9","note":"Federal reference for U.S. customary volume units and conversion relationships used when area and depth become cubic feet."}],"defaultCalculation":{"inputs":{"length":30,"width":15,"shapeFactor":100,"dailyLevelLoss":0.25,"days":7,"coverReduction":0,"refillRate":8,"waterRatePerThousandGallons":0},"result":{"value":"491","unit":"US gallons","label":"Modeled evaporation replacement","lines":[{"label":"Adjusted water surface","value":"450 sq ft"},{"label":"Uncovered evaporation per day","value":"70.13 gal/day"},{"label":"Evaporation depth after cover","value":"1.75 in over 7 days"},{"label":"Water avoided by cover scenario","value":"0 gal"},{"label":"Estimated refill time","value":"61.4 min"},{"label":"Water-only refill cost","value":"Rate not entered"}],"summary":"450 square feet with the entered uncovered evaporation depth represents 491 gallons over 7 days after the 0% cover-reduction scenario.","note":"This scenario applies cover reduction only to the entered evaporation-only baseline. Do not enter total observed pool loss: rain, splash-out, backwashing, overflow, refill equipment, measurement error and leaks require separate accounting."}},"reviewedOn":"2026-07-24","disclaimer":"Planning estimate only. Verify product coverage, supplier rounding, local codes and structural requirements before purchase or construction."}