Grease Duct Velocity Calculator
Check grease duct velocity against code minimums.
Enter your values
Enter the duct airflow in CFM.
Enter the duct width in in.
Enter the duct height in 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.
- Duct velocity
- 1,350 FPM
- Duct area
- 1.78 sq ft
- Code minimum
- 1500 FPM (verify local minimum, some require 1800-2000)
- Status
- Below minimum — reduce duct size or add airflow
Quick answer
Grease ducts must maintain at least 1500 FPM (some jurisdictions require 1800-2000 FPM) to keep grease entrained and moving rather than settling in the duct.
Velocity = CFM / duct cross-sectional area
At a glance
| What it does | Check grease duct velocity against code minimums. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Duct airflow, Duct width, Duct height |
| Main output | Duct velocity |
| Formula | Velocity = CFM / duct cross-sectional area |
| Cost | Free — no sign-up, no download |
How to use the Grease Duct Velocity Calculator
- 1Enter the actual duct airflow (from balancing report or design).
- 2Enter the duct's internal width and height.
- 3Confirm velocity meets or exceeds your jurisdiction's minimum, typically 1500 FPM.
Inputs explained
- Duct airflow(CFM)
- Enter the duct airflow in CFM.
- Duct width(in)
- Enter the duct width in in.
- Duct height(in)
- Enter the duct height in in.
Worked example
Using the values the calculator loads with:
Inputs
- Duct airflow2400 CFM
- Duct width16 in
- Duct height16 in
Results
- Duct velocity1,350 FPM
- Duct area1.78 sq ft
- Code minimum1500 FPM (verify local minimum, some require 1800-2000)
- StatusBelow minimum — reduce duct size or add airflow
Frequently asked questions
What happens below minimum velocity?
Grease settles inside the duct instead of being carried to the filters/exhaust fan, creating a serious fire hazard.
Can duct be oversized instead?
No — oversized grease duct is a common code violation because it drops velocity below the self-cleaning threshold.
What do I need to enter into the Grease Duct Velocity Calculator?
Just 3 values: duct airflow, duct width, duct height. 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 Grease Duct Velocity Calculator work out the answer?
Grease ducts must maintain at least 1500 FPM (some jurisdictions require 1800-2000 FPM) to keep grease entrained and moving rather than settling in the duct. It applies the formula Velocity = CFM / duct cross-sectional area and shows the working so you can check each step by hand.
Is the Grease Duct Velocity 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.