Wet-Bulb Sling Psychrometer

RH, dew point, and GPP from dry-bulb and wet-bulb.

Run the calculator

Example

You enter

Dry-bulb (°F) 80
Wet-bulb (°F) 67

You get

Relative humidity 50.7 %
Dew point 60.1 F
GPP 77.41

Details, formula, and sources

Sling psychrometer dry-bulb / wet-bulb pair → relative humidity, dew point, and grains per pound. Vapor pressure from the psychrometer relation e = e_s(Tw) - A x P x (Td - Tw) with A ≈ 0.000662 1/°C at sea level; saturation vapor pressure e_s by the August-Roche-Magnus approximation.

August-Roche-Magnus formulation by name; ASHRAE Fundamentals psychrometric chart by name.

Psychrometric formulas free in published engineering texts.

Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.

Field names used by the API: dry_bulb_F, wet_bulb_F, RH_percent, dew_point_F, GPP

Atmospheric pressure 14.696 psi (sea level) unless user suppliesNIST