Psychrometric Calculator

Select IP or SI units, enter the dry-bulb temperature, and choose a moisture input: relative humidity, wet-bulb temperature, or dew-point temperature. Then use elevation-derived pressure or enter the actual atmospheric pressure manually.

The calculated air properties and chart marker update from that single air state. You can also click a valid chart location or drag the marker to explore other conditions while keeping the inputs and results synchronized.

Pressure matters because the relationships between temperature, moisture, air density, and other moist-air properties change with atmospheric pressure and elevation.

The horizontal axis shows dry-bulb temperature, and the vertical scale on the right shows humidity ratio. The curved upper boundary is the saturation curve, where relative humidity is 100%.

Relative-humidity curves run through the chart. Other line families represent wet-bulb temperature, enthalpy, and specific volume. The selected point identifies one combination of these related air properties.

A single moist-air state can therefore be described in several ways. Moving the point changes the complete set of properties together.

Dry-bulb temperature

Dry bulb is the ordinary air temperature measured without accounting for evaporative moisture effects.

Wet-bulb temperature

Wet bulb reflects the cooling caused by evaporation and is influenced by both air temperature and moisture content.

For a valid psychrometric state, wet bulb normally cannot exceed dry bulb. As the air approaches saturation, the wet-bulb temperature approaches the dry-bulb temperature.

Relative humidity

Relative humidity compares the air's current water-vapor content with the maximum possible at the same temperature and pressure.

Humidity ratio

Humidity ratio expresses the actual mass of water vapor per unit mass of dry air.

Dew point

Dew point is the temperature at which air reaches saturation when it is cooled without adding or removing moisture.

Because relative humidity changes when temperature changes, dew point is often a more direct indicator of the air's actual moisture content.

Enthalpy

Enthalpy represents the combined thermal energy associated with the dry air and its water vapor.

Specific volume

Specific volume is the volume occupied by the moist-air mixture per unit mass of dry air.

HVAC designers use these properties to compare air states, understand air-conditioning processes, and evaluate how temperature, moisture, energy, and air volume relate to one another.

Start with the calculator's default air state:

Dry-bulb temperature:

75.0°F

Relative humidity:

50.0%

Elevation:

0 ft

Atmospheric pressure:

14.696 psi

The locked psychrometric engine calculates:

Wet-bulb temperature:

62.6°F

Dew-point temperature:

55.1°F

Humidity ratio:

64.6 grains/lb

Enthalpy:

28.1 Btu/lb

Specific volume:

13.68 ft³/lb

On the chart, the point appears at 75°F on the dry-bulb axis and on the 50% relative-humidity curve, below the saturation boundary. The other results describe that same plotted state.

A psychrometric calculator helps compare indoor and outdoor conditions, review cooling and dehumidification, and identify when humidification may be needed.

It can also compare supply-air and room-air states, evaluate air properties at different elevations, and help technicians, designers, engineers, and students visualize how moist-air properties change together.

These comparisons support HVAC analysis, but this guide does not add cooling-load, sensible-heat, latent-heat, air-mixing, or coil-leaving calculations.