Psychrometric chart
A free chart that shows the state of moist air. Give the dry-bulb temperature together with one of relative humidity, wet bulb or dew point. You can also print a blank chart drawn for your own altitude as an A4 or A3 PDF.
How the chart works
The psychrometric chart on this page shows the state of moist air. Saturation pressure is calculated with the Hyland–Wexler equations and the water vapor enhancement factor; barometric pressure is derived from altitude. Click a point on the chart and its dry-bulb and wet-bulb temperatures, dew point, relative humidity, humidity ratio, enthalpy, specific volume and density appear beside it. You can also enter values yourself: give the dry-bulb temperature together with one of relative humidity, wet bulb or dew point.
Calculations follow the altitude or the atmospheric pressure you choose. The default pressure is 101.325 kPa at sea level; when you enter an altitude, the pressure used is shown on screen. The chart covers −10 to +50 °C and can be zoomed; you can switch between SI and IP units.
Two more tools come with the chart. The unit converter handles 18 HVAC quantities, including air flow, water flow, capacity, pressure and temperature difference. The calculator works with the four operations, powers and brackets. The calculator starts closed; open it with the "Calculator" button on the tool's bottom row. Clicking a value on the chart and sending it to the calculator also opens it.
The tool is free. No sign-up and no cookies; only your display preferences (theme and unit) are stored in your browser.
Data note: The values you enter (temperature, humidity, enthalpy, altitude or pressure) and your unit and chart type choices are sent to the iklimet-lab.com server for the calculation. The server runs on our hosting provider Turhost's infrastructure in Istanbul. The calculation software does not store these values. The computed chart drawings (psychrometric and Mollier) are cached for at most 24 hours; point values are not cached; the cache holds no personal data. To limit abuse, a keyed hash (HMAC) of your IP address is kept for at most 2 minutes; the raw IP is not stored for this purpose. Turhost's server access logs, as on any website, contain the IP address, time, requested address and browser information; these logs cannot be turned off, are kept for 6 months, and may remain in Turhost's backups in Turkey for up to 6 more months. Your unit (SI/IP), chart view and line choices are stored only in your browser; the tool does not use cookies. If you choose a theme from the site menu, this preference is also stored only in your browser. Details: Privacy policy.
For reports and history
To save calculations as PDF reports and keep a history, use Psychro Calc Pro:
- Psychro Calc Pro for iPhone
- Psychro Calc Pro for Mac
- Psychro Process Pro — to draw and report the process between two states