What does the IBC require?

Glazing of at least 8% of floor area and openable area of 4% (IBC 1204/1202).

Can I use mechanical ventilation instead?

Yes, the IBC allows mechanical ventilation in lieu of natural.

Bedroom egress windows?

IRC R310: 5.7 sq ft net clear opening (5.0 at grade floor).

Does a patio door count?

Its glazed area does, if it opens outside.

What if a room doesn't comply?

It may not count as a habitable room.

Are kitchens and baths different?

Codes usually allow mechanical ventilation instead.

Daylight and ventilation calculator

Room floor area, glazed and openable area and your code percentages: you get your ratios and the minimum openings required.

Glazing ratio

15 %

Current glazing ratio15 %
Minimum glazed area2 m²
Current openable ratio7.5 %
Minimum openable area1 m²

Use my prices

Your prices per language/currency. Used when you enable “Use my prices” in calculators. My prices →

Calculate labour, margin & GST

How it's calculated (visible formula)

ratio = opening area ÷ floor area; minimum = floor area × required percentage

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure room floor area.
Measure glazed and openable window area.
Enter the percentages your code requires.
Compare current ratios with the minimums.
If short, work out how much opening is missing.

Worked example: 215 sq ft bedroom, 32 sq ft glazing (16 openable)

Light: 15% (minimum 8–10%)
Ventilation: 7.5% (minimum 4–5%)

→ Meets both minimums.

Common mistakes

Counting the frame as glazing.
Using gross instead of net floor area.
Forgetting egress window size requirements in bedrooms.

Pro tips

Measure glass, not the rough opening or frame.
Openings onto small light wells may not count.
Skylights count, often with their own rules.
Pair daylight with shading on south and west faces.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

Create quote Calculate margin & GST

FAQs

What does the IBC require?: Glazing of at least 8% of floor area and openable area of 4% (IBC 1204/1202).
Can I use mechanical ventilation instead?: Yes, the IBC allows mechanical ventilation in lieu of natural.
Bedroom egress windows?: IRC R310: 5.7 sq ft net clear opening (5.0 at grade floor).
Does a patio door count?: Its glazed area does, if it opens outside.
What if a room doesn't comply?: It may not count as a habitable room.
Are kitchens and baths different?: Codes usually allow mechanical ventilation instead.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.