Rain Dilution Calculator
Estimate how rainfall affects your pool chemistry
☔ Rain Dilution Calculator
Estimate how rainfall changes concentration-style readings through dilution. This works for FC, TA, CH, CYA, salt, and TDS. It does not predict pH.
If you know your exact pool surface area, enter it here. Otherwise, we'll estimate based on pool volume and type.
Current readings - optional
How This Tool Works
The calculator estimates how much rainwater entered the pool based on rainfall depth and pool surface area, then applies a dilution model to concentration-style readings such as FC, TA, CH, CYA, salt, and TDS.
Assumptions
- • Rainfall over the pool surface is treated as added fresh water.
- • Concentration-based parameters dilute approximately in proportion to added volume.
- • The pool is assumed to mix reasonably well before you retest.
Important limitations
- • pH is not predicted because acid-base balance does not dilute linearly.
- • Debris, organics, runoff, and circulation problems can matter more than dilution after storms.
- • This tool is a planning aid, not a replacement for post-rain testing.
Formula
Rain volume = surface area × rainfall depth × 0.623 gallons per square foot-inch. Dilution percent = rain volume ÷ new total volume.
Educational guidance only. Verify labels, manuals, local code, and site conditions before acting. Stop for electrical, gas, structural, drain, drowning, injury, emergency, or chemical-mixing risk.