Oval Duct Size Calculator
Flat oval duct equivalent diameter and size.
Enter your values
ⓘ Live results
Results
- Required major axis
- 10 in
- Minor axis (used)
- 6 in
- Approx cross-section area
- 47 sq in
Quick answer
Flat oval duct is described by its major and minor axis, sized to have the same equivalent round diameter as a comparable circular duct.
De = 1.55 x (a x b)^0.625 / (a + b)^0.25 (approx, oval)
How to use the Oval Duct Size Calculator
- 1Enter the round duct diameter the oval duct needs to match for airflow capacity.
- 2Enter the minor axis (height) available for the flat oval, usually set by ceiling space constraints.
- 3Read off the required major axis (width) to keep equivalent capacity.
Worked example
Using the values the calculator loads with:
Inputs
- Target round equivalent diameter10 in
- Minor axis (duct height)6 in
Results
- Required major axis10 in
- Minor axis (used)6 in
- Approx cross-section area47 sq in
Frequently asked questions
Why use flat oval duct?
It fits in shallow ceiling or wall cavities where round duct is too tall, while keeping lower friction than rectangular duct.
Is oval duct more expensive?
Typically yes per linear foot versus round or rectangular, due to specialized fabrication.
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.