Humidity Grains Per Pound Calculator

The Humidity Grains Per Pound Calculator helps you figure out how much moisture is in the air. HVAC technicians use this measurement to determine if a space needs dehumidification. One grain equals 1/7000th of a pound, so the number tells you how many grains of water vapor exist in each pound of dry air.

Quick Example

At 70°F and 50% relative humidity, the air contains about 54 grains of moisture per pound of dry air. That's considered comfortable for most indoor environments. If the GPP goes above 70, the air starts feeling muggy.

Formulas Used

Humidity Ratio Formula

W = 0.62198 × (Pv ÷ (P − Pv))

Where W = humidity ratio, Pv = vapor pressure, P = total atmospheric pressure

Grains Per Pound Formula

Grains Per Pound = Humidity Ratio × 7000

Multiply the humidity ratio by 7000 to convert to grains.

Vapor Pressure Formula

Pv = RH × Psat ÷ 100

Where Psat is the saturation vapor pressure at the given temperature.

How to Use This Calculator

Enter Temperature

Input temperature in Fahrenheit or Celsius

Enter Humidity

Input relative humidity percentage (0-100%)

Get GPP

View grains per pound and other humidity metrics

Grains Per Pound Reference Table

This table shows GPP values for various temperature and humidity combinations:

Temperature (°F)	Relative Humidity	Grains Per Pound	Moisture Level
50°F	30%	16 GPP	Dry
50°F	50%	27 GPP	Normal
60°F	40%	31 GPP	Normal
60°F	60%	46 GPP	Normal
70°F	30%	38 GPP	Normal
70°F	50%	54 GPP	Normal
70°F	70%	76 GPP	High
75°F	40%	50 GPP	Normal
75°F	60%	76 GPP	High
80°F	50%	77 GPP	High
80°F	70%	108 GPP	Very High
85°F	60%	103 GPP	Very High
85°F	80%	137 GPP	Very High
90°F	50%	107 GPP	Very High
90°F	70%	150 GPP	Very High
95°F	60%	144 GPP	Very High
100°F	40%	99 GPP	High
100°F	60%	148 GPP	Very High
40°F	80%	25 GPP	Dry
45°F	60%	23 GPP	Dry
55°F	70%	42 GPP	Normal

Humidity Grains Per Pound Calculator

Humidity GPP Calculator

Environmental Settings

Calculation Results