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.

All calculators
Also see
Application starting
Choose saving method
Download PDF
Download calculate with your chosen settings in PDF format — drawings + data.
Share in social network
Share the link to the calculation on Facebook, Twitter, Google+, etc.
Embed a calculator on your website for FREE

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
Rate this page:
(estimate: 5, votes: 13)