How do I calculate pool water lost to evaporation?

Multiply the pool's surface area by the evaporation depth, using compatible units. This calculator performs that conversion and reports both US gallons and litres.

How does the pool bucket test work?

Expose a partially submerged bucket of pool water and the pool to the same conditions, mark both levels, and compare their drops after the test. If the pool loses more level than the bucket, EPA WaterSense says the pool may have a leak.

How much evaporation can a pool cover prevent?

EPA reports up to 95 percent for solid covers, 50 to 95 percent for solar or bubble covers depending on coverage and shape, and about 15 percent for liquid evaporation suppressants. Real savings depend on effectiveness and hours used.

Does rainfall cancel pool evaporation?

Rain that reaches the pool offsets refill water over the chosen period, but it does not undo the physical evaporation that already occurred. Solid covers, overflow, splash, and drainage can change how much rain is retained.

Does extra pool water loss prove there is a leak?

No. A difference can also reflect measurement error, wind, rain, splash-out, backwashing, autofill operation, or unlike conditions in the pool and bucket. Treat the result as a screening estimate, not a diagnosis.

Are my pool measurements uploaded?

No. Calculations, copying, and CSV creation occur locally in your browser, and the tool does not send or store your input values.

Pool Evaporation & Water Loss Calculator

Turn a measured water-level drop into gallons and litres, estimate pool-cover and rain effects, or compare pool and bucket loss. Inputs stay in your browser.

Pool and measurement

1. Units and surface area

Unit system Pool shape

Length (ft) Width (ft)

2. Measurement method

Evaporation estimate
Use an observed or local depth Bucket-test comparison
Compare two measured drops

Uncovered evaporation depth (in) Editable example—not a climate average. Depth period Analysis days

3. Cover, rain, and other water

Cover type / reduction while used Average cover use (hours/day)

Rainfall during period (in) Rain retained in pool (%) Other known loss (US gal) Splash-out, backwash, or draining over the same period.

4. Optional refill cost

Currency Variable water rate Editable example; use the marginal rate from your bill. Billing unit

Results update as inputs change.

Results

Volume methodSurface area × water-level depth

Bucket interpretationPool drop minus bucket drop

Guidance checkedEPA WaterSense; August 3, 2026

PrivacyNo input upload or storage

How the pool water-loss calculation works

Choose a pool shape and enter its water-surface dimensions.
Enter an observed evaporation depth and period, or switch to the bucket-test comparison.
For an evaporation estimate, add cover use, rain retained, other known losses, and an optional water rate.
Review the water volume, refill requirement, savings, cost, or possible excess loss.

Only the water surface area matters for converting a level change to volume. Pool depth does not enter this calculation. For irregular pools, use a measured or plan-derived custom surface area.

Water volume = pool surface area × water-level depth Covered evaporation = uncovered evaporation × [1 − (cover hours ÷ 24 × cover reduction)] Rain retained = surface area × rainfall × retained percentage Estimated refill = max(0, evaporation − rain retained) + other known loss Possible excess loss in bucket mode = max(0, pool drop − bucket drop) × surface area

The calculator assumes the entered evaporation depth represents an uncovered pool under the conditions being analysed. Cover reduction is applied only for the entered hours. Rain can reduce refill need but does not reduce the reported gross evaporation.

Measurement guidance, assumptions, and limits

Bucket test: EPA WaterSense’s Jump Into Pool Water Efficiency guide describes a 24-hour evaporation bucket test and says greater pool loss than bucket loss may indicate a leak.
Cover performance: EPA’s Pool Water Efficiency guidance reports that pool covers can prevent up to 95% of evaporation. Its commercial pool guidance gives up to 95% for solid covers, 50–95% for solar/bubble covers, and about 15% for liquid suppressants. The 80% solar/bubble starting value here is an editable planning point within that range.
Evaporation input: 0.25 inch/day (6.35 mm/day) is an illustrative starting value, not a local average or forecast. A same-site bucket observation is normally more useful than a generic climate preset because wind, humidity, water temperature, sun, features, and shelter matter.
Cost scope: cost includes only the rate entered. Fixed charges, tiers, sewer rules, chemicals, heating energy, overflow, and repair costs are excluded.

Screening limit: this tool cannot diagnose a leak or locate one. Rain, heavy wind, splashing, backwashing, autofill, measurement error, and different exposure of the bucket and pool can distort a comparison. Investigate persistent excess loss, visible wet areas, air in return lines, or malfunctioning fill equipment with an appropriate pool professional.

Pool evaporation and water-loss FAQ

How do I calculate gallons lost from a pool?

For US units, multiply surface area in square feet by water loss in inches and by 0.623376. A 32 × 16 ft pool losing 0.25 inch loses about 79.8 US gallons before cover effects or rain.

How should I run a bucket test?

Follow EPA’s current guide: choose a day without rain or heavy wind, disable automatic fill and applicable pool systems, close the pool, partially submerge a bucket of pool water, mark both levels, and compare after 24 hours. Follow equipment instructions and do not create an unsafe condition.

Does a larger or deeper pool evaporate faster?

For the same water-level evaporation depth, volume loss scales with surface area—not pool depth. Actual evaporation rate also depends on weather, water temperature, wind, exposure, activity, and features.

How much can a cover save?

EPA reports up to 95% reduction while a suitable cover is in use. Actual period savings also depend on how many hours the cover is deployed and how completely it covers the surface.

Why can rainfall and evaporation both be positive?

They are separate water-balance flows. Water can evaporate and rain can enter during the same week. This tool reports gross evaporation, rain retained, and the net refill need separately.

Does extra loss prove my pool leaks?

No. It is a screening signal. Repeat a controlled test if conditions were poor or measurements uncertain, inspect equipment and the autofill, and seek qualified leak detection for persistent differences.

Are my pool measurements tracked?

No. The calculator does not upload or store input values. Copying and CSV download are created locally in your browser.