Round Duct Area Calculator
Cross-sectional area of a round duct.
Enter your values
ⓘ Live results
Results
- Area
- 50.27 sq in
- In sq ft
- 0.3491
- In m²
- 0.0324
- Circumference
- 25.13 in
Quick answer
Round duct area is pi times the diameter squared divided by four.
A = pi x d² / 4
How to use the Round Duct Area Calculator
- 1Measure the inside diameter of the duct.
- 2Read the area in square feet for airflow maths.
- 3Multiply area by velocity in FPM to get CFM.
Worked example
Using the values the calculator loads with:
Inputs
- Duct diameter8 in
Results
- Area50.27 sq in
- In sq ft0.3491
- In m²0.0324
- Circumference25.13 in
Frequently asked questions
Inside or outside diameter?
Use the inside diameter — that is the air path.
Flex duct?
Use the nominal inside diameter when fully stretched; sag reduces it sharply.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.