Read Axis of Volume per 1kg in Psychrometric Chart

This tutorial will teach you how to calculate air volume when you know other two parameters such as relative humidity, absolute humidity, enthalpy. All these parameters axis are drawn in the psychrometric chart to check.

Example of calculating volume per dry air 1kg using psychrometric chart. Air contains dry air (nitrogen, oxygen, carbon dioxide and more gases) and water vapor. Humidity tells us about water vapor amount. When humidity or temperature of air change volume of dry air changes.

Calculate volume per dry air 1kg


A room exists at 250C. The room can be saturated at 150C. Calculate the volume per 1kg of dry air.


  • Draw a line at 250C of dry bulb temperature(line 1).
  • Draw a line at 150C of wet bulb temperature (line 2).
  • Mark interception point of line 1 & line 2. dry and wet bulb temperatures marking

  • Draw a parallel line to volume (m3)/kg Dry air lines from interception point (line 3).
    Parallel lines are highlighted by red arrows. parellel lines to volume per 1kg

  • Mark interception point of line 3 and bottom axis (line of dry bulb temperature) and name that point as 4.
  • Interception point of volume per dry air 1kg lines (0.85 and 0.90 ) and dry bulb temperature lines are marked as 5 and 6. volume per 1kg lines

  • Measure following distances by a ruler.
    • between points of 5 and 6(x)
    • between points of 5 and 4(y)

  • Then calculate the volume per 1kg of dry air related to our conditions (dry bulb temperature = 250C. wet bulb temperature = 150C. calculate volume per 1kg lines
  • read volume per 1kg psychrometric chart