How to use the diagram
The chart is the phase diagram of water: temperature on the horizontal axis, pressure on a logarithmic vertical axis. The black line is the saturation curve, where liquid water and steam coexist (boiling and condensation). Above it water is liquid, below it water is vapour. The curve ends at the critical point (373.95 °C, 220.64 bar); beyond that temperature and pressure the fluid is supercritical and there is no longer any distinction between liquid and gas.
- Click or tap a point on the diagram — or enter a temperature and pressure in the fields above it.
- Read the phase and all properties in the results panel.
- Change units at any time (°C, K, °F; bar, MPa, kPa, psi, atm; SI or US customary results).
- Use “Copy link to this point” to share or bookmark a state.
Properties returned
For every state the calculator returns density, specific volume, specific enthalpy, internal energy, specific entropy, isobaric and isochoric heat capacities, speed of sound, dynamic and kinematic viscosity, thermal conductivity, Prandtl number and compressibility factor. It also gives the boiling temperature at the chosen pressure and the saturation pressure at the chosen temperature, which tell you how far the state is from boiling.
Enthalpy, internal energy and entropy are relative values: by IAPWS convention, the internal energy and entropy of saturated liquid water are zero at the triple point (0.01 °C).
Reference values
A few states computed by this page, for a quick sanity check against your own steam tables:
| Temperature | Pressure | Phase | Density | Enthalpy | Entropy |
|---|---|---|---|---|---|
| 25 °C | 1 bar | Liquid | 997.05 kg/m³ | 104.93 kJ/kg | 0.36723 kJ/(kg·K) |
| 80 °C | 1 bar | Liquid | 971.8 kg/m³ | 334.99 kJ/kg | 1.0754 kJ/(kg·K) |
| 150 °C | 10 bar | Liquid | 917.3 kg/m³ | 632.57 kJ/kg | 1.8414 kJ/(kg·K) |
| 200 °C | 10 bar | Vapour (steam) | 4.8543 kg/m³ | 2828.3 kJ/kg | 6.6955 kJ/(kg·K) |
| 400 °C | 100 bar | Vapour (steam) | 37.822 kg/m³ | 3097.4 kJ/kg | 6.2139 kJ/(kg·K) |
| 550 °C | 250 bar | Supercritical fluid | 78.522 kg/m³ | 3339.3 kJ/kg | 6.1816 kJ/(kg·K) |
Looking for boiling-point data? See the saturated steam table by temperature and by pressure.
Frequently asked questions
At what temperature does water boil at a given pressure?
Enter the pressure and read “Boiling temperature at this pressure”. At 1 atm (1.01325 bar) water boils at 99.97 °C; at 10 bar it boils at 179.9 °C. The saturated steam table lists the whole curve.
What is the difference between saturated and superheated steam?
Saturated steam is vapour exactly at the boiling temperature for its pressure, i.e. on the saturation curve. Superheated steam is vapour at a temperature above that boiling point — any point below the curve on this diagram.
What is supercritical water?
Above 373.95 °C and 220.64 bar water is a supercritical fluid: its density changes continuously with pressure and temperature and no boiling occurs. The critical density is 322 kg/m³.
Which formulation is used, and how accurate is it?
The page implements the IAPWS Industrial Formulation 1997 (IAPWS-IF97), the international standard used for steam tables and power-plant calculations, plus the IAPWS 2008 viscosity and 2011 thermal-conductivity formulations. The implementation reproduces the verification values published in the IAPWS release. For scientific work requiring the lowest uncertainty, IAPWS recommends the IAPWS-95 formulation instead. Details are on the method and sources page.
What is the valid range?
0 °C to 800 °C for pressures up to 1000 bar, and 800 °C to 2000 °C for pressures up to 500 bar. The diagram shows 0–800 °C; higher temperatures can be typed in the fields. Ice (below 0 °C) is not covered.
Why does 100 °C at 1 atm show vapour?
At 1 atm water boils at 99.97 °C, slightly below 100 °C, so a state at exactly 100 °C and 1.01325 bar is (barely) superheated steam. On the saturation curve itself, liquid and vapour coexist and pressure and temperature alone do not fix the state — use the saturated steam table for those values.