Register Throw Calculator
Estimate register throw distance from velocity.
Enter your values
Enter the register cfm in CFM.
Enter the core (outlet) velocity in FPM.
Choose one of: 150 FPM (high throw), 100 FPM, 50 FPM (typical room).
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.
- Estimated throw
- 4.8 ft
- Core velocity used
- 500 FPM
- Terminal velocity
- 50 FPM
- Guidance
- Match throw to 3/4 of the distance to the opposite wall
Quick answer
Throw is the distance a supply jet travels before slowing to a chosen terminal velocity, commonly 50 or 150 FPM.
Throw ≈ k x sqrt(CFM x core velocity) simplified as core velocity ratio
At a glance
| What it does | Estimate register throw distance from velocity. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Register CFM, Core (outlet) velocity, Terminal velocity |
| Main output | Estimated throw |
| Formula | Throw ≈ k x sqrt(CFM x core velocity) simplified as core velocity ratio |
| Cost | Free — no sign-up, no download |
How to use the Register Throw Calculator
- 1Enter the register CFM and its rated core (outlet) velocity from the catalog.
- 2Pick the terminal velocity that matches your comfort target.
- 3Compare the throw to the room dimensions to avoid drafts hitting occupants directly.
Inputs explained
- Register CFM(CFM)
- Enter the register cfm in CFM.
- Core (outlet) velocity(FPM)
- Enter the core (outlet) velocity in FPM.
- Terminal velocity
- Choose one of: 150 FPM (high throw), 100 FPM, 50 FPM (typical room).
Worked example
Using the values the calculator loads with:
Inputs
- Register CFM120 CFM
- Core (outlet) velocity500 FPM
- Terminal velocity50 FPM (typical room)
Results
- Estimated throw4.8 ft
- Core velocity used500 FPM
- Terminal velocity50 FPM
- GuidanceMatch throw to 3/4 of the distance to the opposite wall
Frequently asked questions
What terminal velocity should I use?
50 FPM is standard for occupied zones; use 150 FPM only for checking maximum reach.
Why does throw matter?
Too little throw leaves stagnant zones; too much can blow directly on people or hit the far wall hard.
What do I need to enter into the Register Throw Calculator?
Just 3 values: register cfm, core (outlet) velocity, terminal velocity. 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 Register Throw Calculator work out the answer?
Throw is the distance a supply jet travels before slowing to a chosen terminal velocity, commonly 50 or 150 FPM. It applies the formula Throw ≈ k x sqrt(CFM x core velocity) simplified as core velocity ratio and shows the working so you can check each step by hand.
Is the Register Throw 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.