How to calculate an air conditioning duct

Installing the correct duct is essential for an efficient air conditioning system. Those who are too large will have a speed air too low in the inside, which will cause it to spend too much time inside the duct, significantly altering the set temperature of the discharge.

Those that are too small have a speed that is very high, which will cause an increase in static pressure and noisy air vents. If the static pressure is too high, the airflow is drastically reduced. Calculate the correct size duct air conditioning is a simple, but important.


  1. Calculate the square meters of the room in which the new conduit will extend. It measures its width and length. Multiply each other to calculate the square meters. For example, a 10×10 foot (0.92 m2) room is 100 square feet (9.29 m2).
  2. Calculate the amount of air you will need in the room. As a general rule, you will need 1 cubic foot per minute (0.03 m3) of air per square foot of space. For example, a room of 100 square meters (9.29 m2) requires 100 cubic feet per minute.
  3. Put the value of cubic feet per minute on an online duct calculator or use a hand duct calculator to calculate the size needed for that room. For example, 100 cubic feet per minute requires a 6 inch (15.24 cm) round duct.