01
The purpose
What does this calculator estimate?
Compare your observed water drop to expected evaporation to judge whether you have a leak.
Water Loss & Leaks · E6
Pool Leak vs. Evaporation Calculator
Compare your observed water drop to expected evaporation to judge whether you have a leak.
Measure the inputsThis tool estimates evaporation from weather so you don't need a bucket — but the bucket test is more direct.
Read the full resultExcess loss over about 0.1 inch a day beyond expected evaporation suggests a leak.
Check the boundaryHot, dry, windy days have high expected evaporation — don't mistake that for a leak.
Useful forWater Loss & LeaksPlanningComparisonVerification
Live calculation
Leak comparison inputs
✓ Checked May 2026
Enter your observed drop and the weather conditions.
Estimated rate
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Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Pool Leak vs. Evaporation Calculator result with context.
Compare your observed water drop to expected evaporation to judge whether you have a leak.
02
The tool
What information does it use?
- Pool surface area: enter a measured or verified value
- Observed drop / 24 hrs: How much the pool actually fell.
- Air temperature: enter a measured or verified value
- Humidity: %
- Wind speed: enter a measured or verified value
03
The method
How to use this calculator
- Pool surface areaEnter the value you can verify.
- Observed drop / 24 hrsHow much the pool actually fell.
- Air temperatureEnter the value you can verify.
- Humidity%
- Wind speedEnter the value you can verify.
04
The relationship
The formula in plain English
Excess loss = Observed drop − Expected evaporation (from weather)
More than ~0.1 inch of excess over 24 hrs points to a probable leak; convert to gallons/day.05
Worked through
A worked example: 0.4" observed drop, mild/moderate weather (≈0.3" expected)
- Expected evap ≈ 0.30 in/24hr
- Excess = 0.4 − 0.3 = 0.1 in
- Borderline → confirm with a bucket test
| Conditions | Expected evap | Observed 0.4 in? | Verdict |
|---|---|---|---|
| Hot, dry, windy | ~0.45 in | 0.4 in | Evaporation |
| Warm, moderate | ~0.30 in | 0.4 in | Possible leak |
| Cool, humid, calm | ~0.12 in | 0.4 in | Probable leak |
| Mild, breezy | ~0.25 in | 0.4 in | Possible leak |
06
Why it matters
How the result supports the next decision
This tool estimates evaporation from weather so you don't need a bucket — but the bucket test is more direct.
Excess loss over about 0.1 inch a day beyond expected evaporation suggests a leak.
07
Good inputs
Improve the estimate before relying on it
- This tool estimates evaporation from weather so you don't need a bucket — but the bucket test is more direct.
- Excess loss over about 0.1 inch a day beyond expected evaporation suggests a leak.
- Hot, dry, windy days have high expected evaporation — don't mistake that for a leak.
- Confirm a suspected leak with a bucket test, then a pressure test of the plumbing.
- Persistent excess loss warrants professional leak detection before it wastes more.
08
The boundary
How to interpret the result
Measurements, equipment specifications, site conditions and local requirements can change the practical result.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
How do I know if my pool is leaking or just evaporating?
Compare how much the pool actually dropped against how much evaporation the weather would explain. If the observed drop is meaningfully larger than expected evaporation — more than about a tenth of an inch a day of excess — a leak is likely. If they match, your loss is just evaporation. A bucket test confirms it directly.
How much water loss points to a leak?
It's the excess over expected evaporation that matters, not the raw drop. On a hot, windy day half an inch may be pure evaporation, while on a cool, humid, calm day even a quarter inch could signal a leak. This tool estimates the expected evaporation for your conditions so you can spot the excess.
Is this as accurate as a bucket test?
It's a fast first check, but the bucket test is more direct because the bucket experiences the exact same weather as your pool, cancelling out estimation error. Use this comparison for a quick read, then confirm anything suspicious with a 24-hour bucket test before calling for leak detection.
What should I do if a leak is likely?
Start with a bucket test to confirm, then narrow the location: compare loss with the pump on versus off to tell pressure-side from structural leaks, and inspect common culprits like the skimmer, light niche, and fittings. If the leak is significant or you can't find it, call a professional leak-detection service.
Can weather fool this comparison?
Yes — that's its main limitation. Very hot, dry, windy conditions produce high real evaporation that the estimate must account for; if your inputs are off, you could misread normal evaporation as a leak or vice versa. Entering accurate temperature, humidity, and wind, then confirming with a bucket test, avoids false alarms.
How can I tell if my pool has a leak?
Compare the observed drop to expected evaporation; excess beyond ~0.1 in/day suggests a leak. Confirm with a bucket test.
How much evaporation is normal per day?
Often a quarter to a half inch in warm or windy weather — more in hot, dry, breezy conditions.
What do I do if my pool is leaking?
Confirm with a bucket test, compare pump-on vs pump-off loss, inspect fittings, then call leak detection if needed.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.