Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Moist Air - Daltons Law of Partial Pressure

The pressure in a mixture of dry air and water vapor - humid or moist air - can be estimated by using Daltons Law of partial pressures.

Sponsored Links

Daltons Law states that

  • the total pressure of a mixture of gases is equal to the sum of the partial pressures of the constituent gases

The partial pressure is the pressure each gas would exert if it alone occupied the volume of the mixture.

Daltons Law of partial pressure for moist air can be expressed as

p = pa + pw                            (1)


p = total pressure of air (Pa, N/m2)

pa = partial pressure dry air (Pa, N/m2)

pw = partial pressure water vapor (Pa, N/m2)

With the partial pressure for dry air and water vapor (1) can be modified to:

p = ρa 286.9 T + ρw 455 T                                    (2)


ρa = density of air (kg/m3)

ρw = density of water vapor (kg/m3)

Sponsored Links

Related Topics

Air Psychrometrics

Moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content.

Related Documents

Moist Air - Specific Volume

Specific volume of moist air is defined as the total volume of humid air per mass unit of dry air

Sponsored Links

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the SketchUp Pro Sketchup Extension Warehouse!

About the Engineering ToolBox!


We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.


This page can be cited as

  • The Engineering ToolBox (2004). Moist Air - Daltons Law of Partial Pressure. [online] Available at: [Accessed Day Month Year].

Modify access date.

. .


3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

6 6

Sponsored Links