Bathroom Fan Fixture Count Calculator
Exhaust fan CFM by bathroom fixtures.
Enter your values
Enter the bathroom area in sq ft.
Enter the toilets you are working with.
Enter the showers/tubs you are working with.
Enter the whirlpool tubs 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.
- Required exhaust
- 100 CFM
- Area-based (1 CFM/sq ft)
- 80 CFM
- Fixture-based total
- 100 CFM
- Duct at 6 in / 700 FPM
- 4 FPM check
Quick answer
Per IMC, add 50 CFM for each toilet, shower or tub and 100 CFM for a whirlpool tub, taking the larger of that total or the area-based rate.
CFM = area x 1 CFM/sq ft, or sum of fixture allowances, whichever is greater
At a glance
| What it does | Exhaust fan CFM by bathroom fixtures. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Bathroom area, Toilets, Showers/tubs, Whirlpool tubs |
| Main output | Required exhaust |
| Formula | CFM = area x 1 CFM/sq ft, or sum of fixture allowances, whichever is greater |
| Cost | Free — no sign-up, no download |
How to use the Bathroom Fan Fixture Count Calculator
- 1Enter bathroom floor area.
- 2Count toilets, showers/tubs and whirlpool tubs.
- 3Use the larger of the area-based and fixture-based results, per IMC 403.
Inputs explained
- Bathroom area(sq ft)
- Enter the bathroom area in sq ft.
- Toilets
- Enter the toilets you are working with.
- Showers/tubs
- Enter the showers/tubs you are working with.
- Whirlpool tubs
- Enter the whirlpool tubs you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Bathroom area80 sq ft
- Toilets1
- Showers/tubs1
- Whirlpool tubs0
Results
- Required exhaust100 CFM
- Area-based (1 CFM/sq ft)80 CFM
- Fixture-based total100 CFM
- Duct at 6 in / 700 FPM4 FPM check
Frequently asked questions
Which method does code use?
IMC allows either the area method (1 CFM/sq ft) or the fixture method — designers use whichever gives more air.
Do I need continuous or intermittent?
Intermittent is common for spot exhaust; continuous low-speed operation is preferred in humid climates.
What do I need to enter into the Bathroom Fan Fixture Count Calculator?
Just 4 values: bathroom area, toilets, showers/tubs, whirlpool tubs. 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 Bathroom Fan Fixture Count Calculator work out the answer?
Per IMC, add 50 CFM for each toilet, shower or tub and 100 CFM for a whirlpool tub, taking the larger of that total or the area-based rate. It applies the formula CFM = area x 1 CFM/sq ft, or sum of fixture allowances, whichever is greater and shows the working so you can check each step by hand.
Is the Bathroom Fan Fixture Count 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.