Toilet Room Exhaust Calculator
Exhaust CFM for a standalone toilet or powder room.
Enter your values
ⓘ Live results
Results
- 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)
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.
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.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.