Check whether a bedroom or basement window meets IRC R310 emergency-escape requirements, including the window well for below-grade openings. Enter the net clear opening and well dimensions.

Net clear opening width (in.)

Net clear opening height (in.)

Sill height above floor (in.)

Window location

Well width (in.)

Well projection from wall (in.)

Well depth (in.)

Net Clear Opening

— sq ft net clear

Must be at least 5.7 sq ft, with the other limits met too.

Usage Tip

Measure the net clear opening with the window fully open, not the frame. If a window is close on area, a casement (which swings fully open) usually beats a hung window of the same size.

THE MATH

Net clear opening area = Width × Height ÷ 144
Required: area ≥ 5.7 sq ft, height ≥ 24″, width ≥ 20″, sill ≤ 44″
Below-grade well: area ≥ 9 sq ft, width and projection ≥ 36″; ladder if depth > 44″

Net clear opening is the actual hole when the window is fully open and operated normally from inside — not the rough opening or the glass. A single- or double-hung window only opens part way, so its net clear height is about half the sash.
Removable screens do not count against the opening; a fixed screen needing tools does.

Every sleeping room needs at least one emergency escape and rescue opening meeting all four window criteria at once — extra area cannot make up for a short height.
IRC 2021 and later use 5.7 sq ft as the universal minimum; some older or amended codes allow 5.0 sq ft for a grade-floor opening. Confirm the edition your jurisdiction enforces.
Below-grade openings need a window well of at least 9 sq ft (36″ projection and width) and a permanently affixed ladder or steps if the well is deeper than 44″. Wells also need drainage. Always confirm with your local building department.