psychart.kr is a free online psychrometric chart for HVAC engineers and engineering students. Click the chart or enter any two values to get dry-bulb, relative humidity, humidity ratio, enthalpy, wet-bulb, dew point, specific volume, density and vapor pressure. Calculations follow ASHRAE Handbook Fundamentals 2017.
A single graph of the state of moist air. The horizontal axis is dry-bulb temperature and the vertical axis is humidity ratio (grams of water vapor per kilogram of dry air). Lines of relative humidity, enthalpy, wet-bulb temperature and specific volume are drawn on top, so knowing any two values lets you read all the others.
It is used for HVAC design, cooling coil and humidifier selection, building environment control and condensation checks.
(1) Dry-bulb is read on the bottom axis along vertical lines, (2) humidity ratio on the right axis along horizontal lines, (3) relative humidity follows the dark red curves rising to the right (the bold black outer curve is 100 %, saturation), (4) enthalpy runs down to the right in green from the scale outside the saturation curve, (5) wet-bulb is the teal dashed line almost parallel to enthalpy, and (6) specific volume is the steep grey-violet dotted line.
The dew point is where a horizontal line from the point meets the saturation curve. In this calculator, hovering shows all values in a card next to the cursor.
It uses the equations of ASHRAE Handbook Fundamentals 2017, chapter 1: Hyland-Wexler saturation pressure, with wet-bulb and dew point solved iteratively rather than approximated.
The engine is our own and is checked automatically against PsychroLib, an open library that implements the same ASHRAE equations: temperatures agree within 0.001 °C and humidity ratio, enthalpy and specific volume within a relative error of 1e-9. For very dry air with a wet-bulb near 0 °C, the water/ice switch in the ASHRAE equations can make the wet-bulb slightly ambiguous.
At 101.325 kPa: humidity ratio 9.88 g/kg, enthalpy 50.3 kJ/kg, wet-bulb 17.9 °C, dew point 13.9 °C, specific volume 0.858 m³/kg, density 1.177 kg/m³ and vapor pressure 1,585 Pa.
Any two independent values among dry-bulb, relative humidity, wet-bulb, dew point, humidity ratio, enthalpy and specific volume (24 combinations). Pairs that carry the same information, such as humidity ratio and dew point, and states above saturation (over 100 % RH) are rejected with the reason.
Example: 30 °C dry-bulb and 22 °C wet-bulb give 50.0 % RH, 18.4 °C dew point and 13.30 g/kg humidity ratio.
Total = dry-air mass flow × (outlet enthalpy − inlet enthalpy), sensible = mass flow × (1.006 + 1.86 × inlet humidity ratio) × temperature difference, latent = total − sensible, condensate = mass flow × humidity ratio difference.
Example: cooling 33 °C/60 % air to 26 °C/50 % at 3,600 kg/h of dry air gives 29.25 kW total, 7.29 kW sensible, 21.96 kW latent, SHF 0.25 and 31.0 kg/h of condensate. At 10,000 CMH (inlet conditions) it is 90.9 kW and 96.4 kg/h.
In this calculator, connect two points and enter the airflow.
Questions or ideas? Use "Feedback" at the top or the community board. Last updated 2026-10-07.