Affected area
Air in the wet room, away from equipment discharge.
—GPP
Dew point —
Vapor pressure —
Vapor pressure —
Free tool · Psychrometric calculator
GPP & dew point calculator for water damage drying
Enter the temperature and relative humidity from your thermo-hygrometer. You get grains per pound, dew point and vapor pressure, and whether the affected area is actually drying.
Unaffected area
Your dry standard: a dry room in the same building.
—GPP
Dew point —
Vapor pressure —
Vapor pressure —
Dehumidifier outlet
Reading at the dehu exhaust grille.
—GPP
Dew point —
Vapor pressure —
Vapor pressure —
Where your readings sit
Curves are relative humidity at sea level. Points higher up the chart hold more moisture.
What the numbers say
How this is calculated
- Saturation vapor pressure uses the Magnus formula (Alduchov–Eskridge constants):
es = 6.1094 · e^(17.625·T / (T + 243.04))hPa, with T in °C. - Actual vapor pressure
pv = es × RH / 100. - Humidity ratio
W = 0.621945 · pv / (P − pv), andGPP = W × 7000(7,000 grains in a pound). - Barometric pressure P is 1013.25 hPa at sea level, adjusted for elevation with the standard atmosphere:
P = 1013.25 · (1 − 2.25577×10⁻⁵ · z)^5.25588, z in meters. Higher elevation means more grains for the same temp and RH, so enter your site elevation if you're well above sea level. - Dew point is the inverse Magnus formula applied to pv.
- Results land within about 1–2 GPP of standard psychrometric charts across normal drying conditions (e.g. 70°F at 50% RH ≈ 54–55 GPP). Your meter's own calculation may differ slightly, so use one method consistently on a job.
Logging these by hand every visit?
RemediDocs records daily atmospheric and moisture readings, calculates GPP for you, tracks equipment, and builds the IICRC S500 drying report your adjuster asks for.
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