Calculator for the Saturation Vapor Pressure

The saturation vapor pressure for water vapor is the pressure at which the water in the air is in a balanced state between solid, liquid and gaseous, i.e. the water neither evaporates nor condenses nor freezes. This is the upper limit for the pressure of the vapor on the air. It increases exponentially with temperature. The saturation vapor pressure can only be calculated for air over a surface of water or ice and this calculation is not very accurate either. Depending on the temperature, air that is over land is roughly comparable to that over water or ice..

Temperature range over water: −45°C to 60°C
Temperature range over ice: −65°C to 0.01°C

The calculation is made using the Magnus formula. This reads:
Saturation vapor pressure over water: E = 6.112 hPa * e ^{17.62 * t / ( 243.12 + t )}
Saturation vapor pressure over ice: E = 6.112 hPa * e ^{22.46 * t / ( 272.62 + t )}
E is the saturation vapor pressure in hectopascals or millibars, e is Euler's number, t is the temperature in degrees Celsius.

Examples: at a temperature of 20 degrees Celsius, the saturation vapor pressure above water is just over 23 millibars. This is an extremely low pressure in the range of a vacuum created with simple means (rough vacuum). At 60 degrees Celsius, the highest value that can be calculated using the Magnus formula, the value is already around 200 millibars. This corresponds roughly to the air pressure at 8,000 meters above sea level, i.e. on the highest mountains in the world, where it is of course well below 60 degrees Celsius.

The saturation vapor pressure is often an auxiliary value when calculating other values, such as the dew point. It plays a role in the theoretical basis for freeze-drying and for cooking under high pressure, as occurs, for example, in the rapid dew process. The saturation vapor pressure is also used in various industrial processes.

Physics commonly uses SI units. Here is a calculator to convert lengths, temperature, pressure, speed and other units.