Bathroom Fan Fixture Count Calculator
Exhaust fan CFM by bathroom fixtures.
Enter your values
ⓘ Live results
Results
- 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
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.
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.
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.