Toilet Room Exhaust Calculator
Exhaust CFM for a standalone toilet or powder room.
Enter your values
Enter the room area in sq ft.
Enter the water closets you are working with.
Choose one of: Intermittent (occupancy sensor), Continuous.
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
- 50 CFM
- Fixture basis
- 50 CFM
- Area basis
- 35 CFM
- Duct at 700 FPM
- 3.6 in dia
Quick answer
Small toilet rooms are commonly exhausted at 50 CFM per water closet intermittent, or 20 CFM continuous, whichever the local code and IMC table require.
CFM = max(50 per WC intermittent, 20 per WC continuous, area x 1)
At a glance
| What it does | Exhaust CFM for a standalone toilet or powder room. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Room area, Water closets, Fan operation |
| Main output | Required exhaust |
| Formula | CFM = max(50 per WC intermittent, 20 per WC continuous, area x 1) |
| Cost | Free — no sign-up, no download |
How to use the Toilet Room Exhaust Calculator
- 1Enter the room area and number of water closets.
- 2Choose intermittent or continuous fan operation.
- 3Take the larger of the fixture-based and area-based airflow.
Inputs explained
- Room area(sq ft)
- Enter the room area in sq ft.
- Water closets
- Enter the water closets you are working with.
- Fan operation
- Choose one of: Intermittent (occupancy sensor), Continuous.
Worked example
Using the values the calculator loads with:
Inputs
- Room area35 sq ft
- Water closets1
- Fan operationIntermittent (occupancy sensor)
Results
- Required exhaust50 CFM
- Fixture basis50 CFM
- Area basis35 CFM
- Duct at 700 FPM3.6 in dia
Frequently asked questions
Do I need makeup air for a small toilet room?
Usually the undercut door provides enough transfer air; no dedicated makeup air unit is needed at this scale.
Continuous vs intermittent?
Continuous low-CFM operation controls odour better in commercial restrooms with steady traffic.
What do I need to enter into the Toilet Room Exhaust Calculator?
Just 3 values: room area, water closets, fan operation. 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 Toilet Room Exhaust Calculator work out the answer?
Small toilet rooms are commonly exhausted at 50 CFM per water closet intermittent, or 20 CFM continuous, whichever the local code and IMC table require. It applies the formula CFM = max(50 per WC intermittent, 20 per WC continuous, area x 1) and shows the working so you can check each step by hand.
Is the Toilet Room Exhaust 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.