basic

Bathroom Vent-Fan CFM by Area Calculator

CFM ≈ area · ceiling_height · 8 ACH / 60.

Size a bathroom exhaust fan in CFM using the Home Ventilating Institute target of 8 air changes per hour: CFM = area_sq_ft · ceiling_height_ft · 8 / 60. Reports the raw computed CFM and the practical recommended fan size (rounded up to common sizes 50/70/90/110/150 CFM with a 50 CFM minimum for any bathroom).

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

sq ft
ft

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

CFM = area · height · 8 / 60.

In depth

Size a bathroom exhaust fan in CFM using the Home Ventilating Institute target of 8 air changes per hour: CFM = area_sq_ft · ceiling_height_ft · 8 / 60. Reports the raw computed CFM and the practical recommended fan size (rounded up to common sizes 50/70/90/110/150 CFM with a 50 CFM minimum for any bathroom).