Interactive Psychrometric Chart

Reading the chart

The horizontal axis is dry bulb temperature and the vertical axis is water vapour mass per kilogram of dry air. Curves show relative humidity in steps of 10 percent. Pressure applies to all curves and states. Both axes can be adjusted. Points outside the axes remain in the table and are flagged.

States and processes

Enter temperature with relative humidity or humidity ratio to add a state. Click or touch the chart to read that location. Arrow keys move the cursor and Enter adds the selected state. States above the saturation curve are rejected. Choose a start and end state to calculate enthalpy and humidity ratio differences. Heating perfectly dry air by 10 °C requires 10.06 kJ per kilogram.

Limits

This is an ideal moist air model. Enthalpy and humidity ratio are per kilogram of dry air. Sensible energy is calculated at the inlet humidity ratio. Latent energy is the remaining enthalpy difference. Enter a dry air mass flow to convert these differences into heat rates. For volume flow, mass flow = volume flow / v. Use the table value of v at the state where volume flow was measured. Liquid condensate energy and equipment efficiency are excluded. Constant enthalpy and wet bulb lines are not displayed. This is not an equipment sizing tool.

Frequently asked questions

How do you calculate humidity ratio from relative humidity?

For example, at dry bulb temperature 30 °C, relative humidity 50 percent and absolute pressure 101325 Pa, humidity ratio is 13.31 g/kg of dry air. Obtain water vapour partial pressure from saturation pressure and relative humidity, then use the ideal moist air relation, excluding equipment efficiency and energy carried by condensed liquid.

Calculate with these values