Air Changes Per Hour Calculator
Ventilation rate for a room.
Enter your values
Enter the room length in ft.
Enter the room width in ft.
Enter the ceiling height in ft.
Enter the airflow in CFM.
Enter the target ach you are working with.
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.
- Air changes per hour
- 5.56
- Room volume
- 2,700 ft³
- CFM for target ACH
- 270
- Status
- Below target
Quick answer
Air changes per hour measures how many times a room's air volume is replaced each hour.
ACH = CFM × 60 ÷ room volume
At a glance
| What it does | Ventilation rate for a room. |
|---|---|
| Category | Engineering |
| Inputs needed | Room length, Room width, Ceiling height, Airflow, Target ACH |
| Main output | Air changes per hour |
| Formula | ACH = CFM × 60 ÷ room volume |
| Cost | Free — no sign-up, no download |
How to use the Air Changes Per Hour Calculator
- 1Enter the room dimensions.
- 2Enter the measured or designed airflow.
- 3Set the ACH target for the room type.
Inputs explained
- Room length(ft)
- Enter the room length in ft.
- Room width(ft)
- Enter the room width in ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
- Airflow(CFM)
- Enter the airflow in CFM.
- Target ACH
- Enter the target ach you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Room length20 ft
- Room width15 ft
- Ceiling height9 ft
- Airflow250 CFM
- Target ACH6
Results
- Air changes per hour5.56
- Room volume2,700 ft³
- CFM for target ACH270
- StatusBelow target
Frequently asked questions
What ACH does a kitchen need?
Typically 7–8; bathrooms 6–8 and offices 4–6.
Does higher ACH cost more?
Yes — in fan energy and conditioned air lost.
What do I need to enter into the Air Changes Per Hour Calculator?
Just 5 values: room length, room width, ceiling height, airflow, target ach. 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 Air Changes Per Hour Calculator work out the answer?
Air changes per hour measures how many times a room's air volume is replaced each hour. It applies the formula ACH = CFM × 60 ÷ room volume and shows the working so you can check each step by hand.
Is the Air Changes Per Hour 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.