Natural Ventilation Opening Calculator
Window area for natural ventilation.
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ⓘ Live results
Results
- Openable area required
- 8 sq ft
- Gross window area needed
- 16 sq ft
- As % of floor
- 4%
- Typical airflow at 8 mph wind
- 1,971 CFM
- Note
- Openings on two sides roughly double the flow
Quick answer
Most codes require openable area of at least 4-5% of the floor area for natural ventilation.
openable area = floor area x required percentage
How to use the Natural Ventilation Opening Calculator
- 1Measure the room floor area.
- 2Check your local code percentage — 4% is common, 5% in some jurisdictions.
- 3Remember a sliding sash only opens half its gross area.
Worked example
Using the values the calculator loads with:
Inputs
- Floor area200 sq ft
- Required percentage4 %
- Window openable fraction50 %
Results
- Openable area required8 sq ft
- Gross window area needed16 sq ft
- As % of floor4%
- Typical airflow at 8 mph wind1,971 CFM
- NoteOpenings on two sides roughly double the flow
Frequently asked questions
Does a skylight count?
Only if it opens; fixed glazing counts toward light requirements but not ventilation.
Single-sided rooms?
Effective depth is limited to about 2.5 times ceiling height from the window.
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.