High-Wall Register Size Calculator
Size a high sidewall supply register.
Enter your values
Enter the register cfm in CFM.
Enter the face velocity in FPM.
Enter the free area fraction in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Required free area
- 0.217 sq ft
- Gross opening size
- 0.289 sq ft
- Approx size
- 6.4 x 6.4 in
- Suggested throw check
- Aim for throw ≈ 3/4 of room width
Quick answer
High sidewall registers are commonly designed for 500-700 FPM face velocity since throw across the ceiling plane matters more than at floor level.
Free area = CFM / face velocity
At a glance
| What it does | Size a high sidewall supply register. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Register CFM, Face velocity, Free area fraction |
| Main output | Required free area |
| Formula | Free area = CFM / face velocity |
| Cost | Free — no sign-up, no download |
How to use the High-Wall Register Size Calculator
- 1Enter the register's design CFM.
- 2Use 500-700 FPM, higher than floor registers, since the jet needs to travel and mix near the ceiling.
- 3Verify the resulting throw with the register throw calculator.
Inputs explained
- Register CFM(CFM)
- Enter the register cfm in CFM.
- Face velocity(FPM)
- Enter the face velocity in FPM.
- Free area fraction(%)
- Enter the free area fraction in %.
Worked example
Using the values the calculator loads with:
Inputs
- Register CFM130 CFM
- Face velocity600 FPM
- Free area fraction75 %
Results
- Required free area0.217 sq ft
- Gross opening size0.289 sq ft
- Approx size6.4 x 6.4 in
- Suggested throw checkAim for throw ≈ 3/4 of room width
Frequently asked questions
Why higher velocity than floor registers?
High sidewall registers rely on the Coanda effect along the ceiling for mixing, needing more velocity to carry that far.
Floor or high sidewall — which is better?
It depends on climate and duct routing; high sidewall suits cooling-dominant climates, floor suits heating-dominant ones.
What do I need to enter into the High-Wall Register Size Calculator?
Just 3 values: register cfm, face velocity, free area fraction. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the High-Wall Register Size Calculator work out the answer?
High sidewall registers are commonly designed for 500-700 FPM face velocity since throw across the ceiling plane matters more than at floor level. It applies the formula Free area = CFM / face velocity and shows the working so you can check each step by hand.
Is the High-Wall Register Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.