Garage Ventilation CFM Calculator
Exhaust fan size for a garage or workshop.
Enter your values
Enter the garage length in ft.
Enter the garage width in ft.
Enter the ceiling height in ft.
Choose one of: Parking and storage, Workshop / hobby, Engines running or spraying.
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.
- Exhaust fan size
- 500 CFM
- Air changes used
- 6 ACH
- Garage volume
- 4,752 cu ft
- Intake opening needed
- 137 sq in
Quick answer
Garages usually need 6–12 air changes per hour, rising to 20 or more where engines run or solvents are used.
CFM = garage volume x ACH / 60
At a glance
| What it does | Exhaust fan size for a garage or workshop. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Garage length, Garage width, Ceiling height, Main use |
| Main output | Exhaust fan size |
| Formula | CFM = garage volume x ACH / 60 |
| Cost | Free — no sign-up, no download |
How to use the Garage Ventilation CFM Calculator
- 1Measure the garage and enter the dimensions.
- 2Pick the use case — running engines demand far more air.
- 3Fit the exhaust high and the intake low on the opposite wall.
Inputs explained
- Garage length(ft)
- Enter the garage length in ft.
- Garage width(ft)
- Enter the garage width in ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
- Main use
- Choose one of: Parking and storage, Workshop / hobby, Engines running or spraying.
Worked example
Using the values the calculator loads with:
Inputs
- Garage length24 ft
- Garage width22 ft
- Ceiling height9 ft
- Main useParking and storage
Results
- Exhaust fan size500 CFM
- Air changes used6 ACH
- Garage volume4,752 cu ft
- Intake opening needed137 sq in
Frequently asked questions
Is a window enough?
Not when engines run. Carbon monoxide needs mechanical extraction with make-up air.
Where should the fan go?
High on the wall furthest from the intake so air sweeps across the whole space.
What do I need to enter into the Garage Ventilation CFM Calculator?
Just 4 values: garage length, garage width, ceiling height, main use. 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 Garage Ventilation CFM Calculator work out the answer?
Garages usually need 6–12 air changes per hour, rising to 20 or more where engines run or solvents are used. It applies the formula CFM = garage volume x ACH / 60 and shows the working so you can check each step by hand.
Is the Garage Ventilation CFM 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.