How to calculate cfm for ducts

Written by c. taylor
  • Share
  • Tweet
  • Share
  • Pin
  • Email
How to calculate cfm for ducts
Calculate the cubic feet per minute of airflow in ducts. (rohr image by Bergmeister from Fotolia.com)

Air flow, usually calculated in cubic feet per minute (CFM), can be calculated by the area of a duct's cross section and the velocity of the air itself. You may be able to reference the velocity, but if not, a device may be required to measure it for you. These devices measure velocity based on pressure. Assuming you can acquire the necessary data, calculating the CFM is relatively painless.

Skill level:
Easy

Other People Are Reading

Things you need

  • Tape measure

Show MoreHide

Instructions

  1. 1

    Measure two consecutive sides of the duct, in inches.

  2. 2

    Convert inches into feet by dividing each measurement by 12.

  3. 3

    Calculate the cross-sectional area of the duct by multiplying the two numbers together.

  4. 4

    Multiply the cross-sectional area by the air velocity, measured in feet per minute, to calculate air flow in CFM.

  1. 1

    Measure the diameter of the opening.

  2. 2

    Convert the measurement into inches by dividing it by 12.

  3. 3

    Divide the diameter by two to calculate the radius.

  4. 4

    Square the radius and multiple it by PI, or 3.14, to calculate the area.

  5. 5

    Multiply the area by the air velocity, measured in feet per minute, to calculate air flow in CFM.

Don't Miss

Filter:
  • All types
  • Articles
  • Slideshows
  • Videos
Sort:
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the eHow.co.uk site, you consent to the use of cookies. For more information, please see our Cookie policy.