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Psychrometric state chart
Plot relative-humidity curves at an absolute pressure and compare two moist-air states.
Inputs
Inputs and calculations are processed in this browser.
Moist-air chart
The horizontal axis is dry-bulb temperature and the vertical axis is water vapor per kg of dry air. Curves represent 10% to 100% relative humidity in 10% increments; A and B are the entered states.
Scroll the chart horizontally on narrow screens.
One or both states exceed the selected humidity-ratio axis and are not drawn. Increase the axis maximum to show them; the full results remain in the table.
After editing inputs, select Update chart.
After editing inputs, select Update chart.
State-point results
| Property | A | B |
|---|---|---|
| Humidity ratio (g/kg) | ||
| Specific enthalpy (kJ/kg) | ||
| Dew / frost point (°C) | ||
| Wet bulb (°C) | ||
| Specific volume (m³/kg) |
Enthalpy, humidity ratio and specific volume are per unit mass of dry air.
Chart and calculation method
Dry-bulb temperature is plotted horizontally and humidity ratio vertically. Curves use PsychroLib’s relative-humidity convention; they are sampled every 0.5 °C, joined by straight segments, and clipped to the selected vertical range. Points are calculated from temperature and relative humidity. This chart does not draw process, enthalpy or wet-bulb lines or simulate mixing, condensation or frost.
Phase convention and limits
Pressure is absolute, not gauge. At dry-bulb temperatures ≤ 0.01 °C relative humidity uses ice saturation; above that it uses liquid-water saturation. A dew/frost point ≤ 0.01 °C is a frost point. Wet-bulb calculations switch between ice and water branches at 0 °C; near freezing, assumptions can materially affect results. Curves and points are approximate; displayed digits do not imply accuracy.
Software license and related tools
Calculations use PsychroLib 2.5.0, Copyright © 2018–2020 PsychroLib Contributors, under the MIT License. MIT License · PsychroLib
Results use a common model reference state. Verify critical designs against actual conditions and applicable standards.