Enter your pool shell's measurements and today's conditions, and we'll tell you how many liters you're losing per day to evaporation, using the real formula the industry uses, not a generic estimate. That way you'll know whether what you're losing is normal, or whether it's worth suspecting a leak.
We use the evaporation formula for outdoor pools, based on the pool shell's surface area, the humidity difference between the water and the air, and the effect of wind.
Fill in the measurements, temperatures and humidity to calculate.
0 LLiters evaporated per day (estimated)
0 cmLevel drop per day
Within normal rangeThis level of evaporation falls within the usual range for an outdoor pool.
If you're losing considerably more than this on a sustained basis, don't rule out a real leak, the bucket test settles it in 24 hours, with no need to call anyone.
Pool shell surface area
The more water surface exposed to the air, the more it evaporates, it's the heaviest-weighted of the four factors.
Temperature difference
The warmer the water is compared to the air, the faster it turns to vapor.
Air humidity
With the air already saturated with moisture, the water struggles to evaporate more, that's why it's less noticeable on humid days.
Wind
Wind renews the air right above the water, so it speeds up evaporation even if neither the temperature nor the humidity changes.
Escucha esta guíaIdeal si tienes las manos ocupadas junto a la piscina
Why these 4 factors, and not a fixed figure
It's common to see the typical line "a pool loses between 3,000 and 7,000 liters a month", but that figure isn't much use, because the real evaporation of your specific pool depends on these 4 factors at once, not on a generic average. A 10x5 m pool on a dry, windy day can evaporate in one afternoon what another, smaller pool on a humid, calm day loses in an entire week.
How we interpret the result
As a general reference, an outdoor pool that isn't in use usually loses between 2.5 and 3.75 cm of level per week to normal evaporation. If the calculator's result stays within that range, there's nothing to worry about, it's physics, not a fault. If it clearly and consistently exceeds that over several days, then it's worth investigating further.
What to do if you're losing more than the calculator shows
Before thinking about a leak, check there isn't a simpler explanation: a recent backwash, splashing from bathers, or simply an unusually windy and hot day. If you rule all that out and the level keeps dropping more than expected, the bucket test confirms it in 24 hours with no need to call anyone, and if it's confirmed, you'll know it's time to check the joints, skimmer or the pool shell structure itself.
Frequently asked questions
Yes, noticeably, by covering the water surface, it cuts off direct contact with the air, which is exactly what drives evaporation. It's the single most effective measure if the issue concerns you.
Because summer combines all 4 factors against you at once: a bigger gap between the water temperature and the night-time air, lower ambient humidity on many days, and more hours of sun and wind acting on the surface.
It's designed for outdoor pools. Indoor pools have their own formula, because the air isn't renewed in the same way and dehumidification and room ventilation come into play.
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