Diffuser Throw Calculator
Air throw distance and spacing for diffusers.
Enter your values
Enter the airflow per diffuser in CFM.
Choose one of: 4-way ceiling, 2-way ceiling, Linear slot, Sidewall register.
Enter the distance to wall in ft.
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.
- Throw distance
- 12.7 ft
- Target throw (75% of distance)
- 9 ft
- Fit
- Good coverage
- Suggested spacing
- 17.8 ft
- Airflow
- 200 CFM
Quick answer
Diffuser throw is the distance air travels before slowing to 50 FPM, and it should reach roughly three-quarters of the way to the wall.
throw ≈ K x sqrt(CFM) for the diffuser type
At a glance
| What it does | Air throw distance and spacing for diffusers. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Airflow per diffuser, Diffuser type, Distance to wall |
| Main output | Throw distance |
| Formula | throw ≈ K x sqrt(CFM) for the diffuser type |
| Cost | Free — no sign-up, no download |
How to use the Diffuser Throw Calculator
- 1Enter the airflow each diffuser handles and pick the type.
- 2Compare the throw to about three-quarters of the distance to the opposite wall.
- 3Space diffusers at roughly 1.4 times the throw for even coverage.
Inputs explained
- Airflow per diffuser(CFM)
- Enter the airflow per diffuser in CFM.
- Diffuser type
- Choose one of: 4-way ceiling, 2-way ceiling, Linear slot, Sidewall register.
- Distance to wall(ft)
- Enter the distance to wall in ft.
Worked example
Using the values the calculator loads with:
Inputs
- Airflow per diffuser200 CFM
- Diffuser type4-way ceiling
- Distance to wall12 ft
Results
- Throw distance12.7 ft
- Target throw (75% of distance)9 ft
- FitGood coverage
- Suggested spacing17.8 ft
- Airflow200 CFM
Frequently asked questions
What happens with short throw?
Air dumps straight down, creating cold spots under the diffuser and stagnant zones at the perimeter.
Heating vs cooling?
Warm supply air is buoyant and throws less, so perimeter throw matters most in heating.
What do I need to enter into the Diffuser Throw Calculator?
Just 3 values: airflow per diffuser, diffuser type, distance to wall. 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 Diffuser Throw Calculator work out the answer?
Diffuser throw is the distance air travels before slowing to 50 FPM, and it should reach roughly three-quarters of the way to the wall. It applies the formula throw ≈ K x sqrt(CFM) for the diffuser type and shows the working so you can check each step by hand.
Is the Diffuser 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.