Floor Register Size Calculator
Size a floor supply register.
Enter your values
ⓘ Live results
Results
- Required free area
- 0.222 sq ft
- Gross opening size
- 0.317 sq ft
- Approx size
- 6.8 x 6.8 in
Quick answer
Floor registers are commonly sized for 400-500 FPM face velocity since air exits close to occupants and must stay gentle.
Free area = CFM / face velocity
How to use the Floor Register Size Calculator
- 1Enter the floor register's design CFM.
- 2Use a lower velocity, 400-500 FPM, so the jet does not blow directly on feet.
- 3Size the opening from the free-area fraction and compare it against standard floor register stock sizes.
Worked example
Using the values the calculator loads with:
Inputs
- Register CFM100 CFM
- Face velocity450 FPM
- Free area fraction70 %
Results
- Required free area0.222 sq ft
- Gross opening size0.317 sq ft
- Approx size6.8 x 6.8 in
Frequently asked questions
Why lower velocity for floor registers?
They are close to occupants standing or sitting nearby, so a gentler jet avoids drafts.
Are floor registers good for cooling?
Cold air naturally sinks, so floor supply can struggle to mix in cooling mode compared with ceiling or high sidewall supply.
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.