Steam tables and h-s (Mollier) chart online (IAPWS-IF97)

Properties of water and steam from any pair: pressure and temperature, p and h, p and s, p and quality x, t and x, h and s. The calculator finds the region (liquid, wet or superheated steam), computes v, ρ, h, s, u, cp, cv and plots the point on the h-s chart. Add a process: adiabatic expansion in a turbine with efficiency, or throttling. Below is a saturation table with a step and copying to Excel.

Saturated water and steam table

ArgumentFrom, °CTo, °CStep, °C

tₛ, °C	pₛ, MPa	v′, m³/kg	v″, m³/kg	h′, kJ/kg	h″, kJ/kg	r, kJ/kg	s′, kJ/(kg·K)	s″, kJ/(kg·K)
0	6.11213·10⁻⁴	0.00100021	206.14	−0.0415878	2500.89	2500.93	−1.5455·10⁻⁴	9.15576
10	0.00122818	0.00100035	106.309	42.0211	2519.23	2477.21	0.151085	8.89985
20	0.00233921	0.00100184	57.7615	83.9199	2537.47	2453.55	0.296503	8.66612
30	0.00424669	0.00100441	32.8816	125.745	2555.58	2429.84	0.436793	8.45211
40	0.00738443	0.00100788	19.517	167.541	2573.54	2406	0.57243	8.25567
50	0.0123513	0.00101214	12.0279	209.336	2591.31	2381.97	0.703794	8.07491
60	0.0199458	0.00101711	7.66766	251.154	2608.85	2357.69	0.831216	7.90817
70	0.0312006	0.00102276	5.03973	293.018	2626.1	2333.08	0.954993	7.75399
80	0.0474147	0.00102904	3.40527	334.949	2643.01	2308.07	1.07539	7.61102
90	0.0701824	0.00103594	2.35915	376.968	2659.53	2282.56	1.19266	7.47807
100	0.101418	0.00104346	1.67186	419.099	2675.57	2256.47	1.30701	7.35408

What the calculator does

Water and steam properties follow the industrial formulation IAPWS-IF97 (International Association for the Properties of Water and Steam, Revised Release R7-97(2012)), the standard behind modern steam tables and Mollier charts. The coefficients were transferred from the official IAPWS text, and the code is checked against the verification tables of the formulation itself: 72 property values (18 each in tables 5, 15, 33 and 42 for regions 1, 2, 3 and 5) and 6 saturation points (tables 35 and 36) match in all 9 significant digits.

IAPWS-IF97 regions

Region 1: liquid water from 0 to 350 °C above the saturation pressure, up to 100 MPa. Gibbs free energy g(p, T).
Region 2: steam from 0 to 800 °C below the saturation pressure (and below the B23 boundary at 350…590 °C). Gibbs free energy with ideal-gas and residual parts.
Region 3: the near-critical zone (350…590 °C, high pressures). Helmholtz free energy f(ρ, T); density from p and T is found iteratively.
Region 4: the saturation line from 0 °C to the critical point (373.946 °C, 22.064 MPa), equations p_s(T) and T_s(p). Wet steam is a mixture of saturated liquid and vapor with quality x.
Region 5: steam from 800 to 2000 °C up to 50 MPa.

Backward problems

The IF97 basic equations use (p, T) or (ρ, T). For (p, h) and (p, s) the temperature is found by iteration (regula falsi with bisection); for (h, s) the pressure is found too, since at constant s the enthalpy grows monotonically with pressure. IF97 also provides fast backward equations T(p, h) and T(p, s), but they differ from the basic equations by hundredths of a kelvin; iteration gives an answer consistent with the basic equations.

Processes on the h-s chart

Turbine expansion. The ideal process is the isentrope 1–2s: s₂s = s₁, enthalpy drop H₀ = h₁ − h₂s. With isentropic efficiency η: h₂ = h₁ − η·H₀, work l = h₁ − h₂, power N = G·l.
Throttling (valve): h₂ = h₁, a horizontal line on the h-s chart; pressure falls, entropy rises, superheated steam usually cools.

Example

Steam at 10 MPa, 500 °C: h₁ = 3375.1 kJ/kg, s₁ = 6.5993 kJ/(kg·K). Expansion to 10 kPa: the isentropic end is wet, x₂s = 0.793, h₂s = 2089.6 kJ/kg, H₀ = 1285.4 kJ/kg. With η = 0.85: h₂ = 2282.5 kJ/kg, x₂ = 0.874, l = 1092.6 kJ/kg; at G = 100 kg/s the power is about 109 MW.

Limitations

Accuracy is that of IF97 itself (a fraction of a percent or better for most properties). Metastable states (subcooled vapor, superheated liquid) and ice are not covered. Very close to the critical point (within fractions of a kelvin of 373.946 °C) the two-phase values v′, v″ come from the region 3 equation and are less accurate. Viscosity, thermal conductivity and surface tension are separate IAPWS formulations and are not included.

Sources: IAPWS R7-97(2012), Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam, iapws.org; W. Wagner, A. Kruse, Properties of Water and Steam, Springer, 1998.

FAQ

How do I find steam enthalpy from pressure and temperature?

Choose the pair p, t, pick the units and enter the values. For example, 10 MPa and 500 °C give superheated steam with h = 3375.1 kJ/kg and s = 6.5993 kJ/(kg·K). If the temperature is below the saturation temperature at that pressure, the state is liquid water (region 1).

How do I find the quality of wet steam?

Enter pressure and enthalpy (or entropy). If the value lies between h′ and h″, the steam is wet and x = (h − h′)/(h″ − h′). The calculator shows x and the wet steam region. The other way round, the pair p, x or t, x gives h, s and v of the mixture.

How do I calculate turbine work with efficiency?

Choose Turbine expansion, set the inlet state, the outlet pressure p₂ and the isentropic efficiency η. The calculator finds the isentropic end 2s (s = const), the enthalpy drop H₀ = h₁ − h₂s, the actual enthalpy h₂ = h₁ − η·H₀ and the work l = h₁ − h₂. Enter the flow G to get the power N = G·l.

Why does steam cool down when throttled?

Throttling involves no heat or work, so h₂ = h₁. For real steam the enthalpy depends on pressure as well as temperature (the Joule–Thomson effect), so superheated steam cools as the pressure drops. Wet steam gets drier. Entropy always rises.

How accurate is it, and how does IF97 differ from IAPWS-95?

IAPWS-95 is the scientific formulation: the most accurate, but slow. IF97 is the industrial one: it reproduces IAPWS-95 within measurement uncertainty and is the standard for power plant calculations. This implementation is checked against the IF97 verification tables: 80 check values (properties in regions 1, 2, 3, 5, the saturation line and the B23 boundary) match in all 9 significant digits.