Water-Steam Equilibrium Vapor Pressure

The Water-Steam Equilibrium Vapor Pressure calculator uses the Antoine Equation to compute the pressure where water vapor is in equilibrium with liquid water.

INSTRUCTIONS: Choose units and enter the following:

• (T) Temperature of Steam

Equilibrium Vapor Pressure (P): The calculator returns the pressure in kilopascals (kPa).  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The formula for the vapor pressure of steam in equilibrium with liquid water is:

`log_"10" P = A - B/(T -C)`

where:

• P = Equilibrium vapor pressure
• T = Temperature
• For T between 273K and 333K
  • A = 7.2326
  • B = 1750.286
  • C = 38.1
• For T between 333K to 423K 
  • A = 7.0917
  • B = 1668.21
  • C = 45.1

The above is a form of the Antoine Equation with constants set for liquid water and water vapor.