Air Duct Calculator

Air Duct Calculator

KALK.PRO's duct calculator will help you estimate the required duct size of the ventilation system for quality air exchange in the room.

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On this page you can estimate the size of the ducts for the correct functioning of the ventilation system. The tool helps to calculate the cross-sectional area of the ducts according to the values of air exchange and air velocity of the air flow. Please note that the recommended velocity for residential areas is 3-5 m/s (but no more than 10 m/s). The required parameters for the calculation can be seen on the notation below. To get the result, click the "Calculate" button.


How to calculate the cross-sectional air duct area?

Formula cross-sectional air duct area: S (m2) = L / (3600 × V)

  • L – indoor air exchange, m3/h;
  • V – air velocity, m/s.

Formula for calculating rectangular duct side (at A=B): A (mm) = 1000 × √S
Formula for calculating round duct diameter: D (mm) = 1000 × 2 × √(S / 3.14)

  • L – cross-sectional area, m2.


Recommended values of air velocity in the ventilation system, m/s

Supply grilles2.0-2.52.0-2.52.5-6.0
Main air ducts3.5-5.03.5-6.06.0-11.0
Air filters1.2-1.51.5-1.81.5-1.8
Heat exchangers2.2-2.52.5-3.02.5-3.0


Straight rectangular duct section
Straight circular duct section
Rectangular duct bend
Circular duct bend
Rectangular duct adapter
Circular duct adapter
Round-to-rectangular ducting adapter
Tee for rectangular ducts
Tee for circular ducts
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