Egress Window Calculator

This egress window calculator checks whether a bedroom or basement window can serve as an emergency escape and rescue opening under the International Residential Code (IRC). Enter the net clear opening width and height — the actual open space you could climb through with the sash fully open — plus the sill height, and it tests the opening area, minimum width, minimum height and maximum sill height, then checks the window well if the sill is below grade.

It is for homeowners finishing a basement, buyers checking whether a “bedroom” is legally a bedroom, and contractors choosing a replacement window. The rules used are the IRC minimums for emergency escape and rescue openings: at least 5.7 sq ft of net clear opening (5.0 sq ft for grade-floor openings), at least 24 inches high and 20 inches wide, a sill no more than 44 inches above the floor, and window wells of at least 9 sq ft with 36 inches of width and projection, with a permanent ladder or steps once a well is deeper than 44 inches.

The rules are taken from the 2021 IRC, Section R310, and are unchanged in the 2024 IRC, where the section is renumbered R319. A grade-floor opening is one whose sill (the bottom of the clear opening) is no more than 44 inches above or below the finished ground outside; it needs only 5.0 sq ft. Deeper basement windows and upper-floor windows need 5.7 sq ft. Your state or city may use an older edition or local amendments, so confirm with your building department before buying a window.

Net clear opening is the unobstructed space when the window is opened normally from inside — for a casement that is the clear width and height with the sash swung open, for a double-hung or slider only the open half counts. Multiply clear width by clear height in inches and divide by 144 to get square feet. The IRC requires every emergency escape and rescue opening to have at least 5.7 sq ft (5.0 sq ft at grade-floor level), and independently at least 24 inches of clear height and 20 inches of clear width, so a 20 × 24 opening (3.3 sq ft) is not enough on its own: one dimension must be larger.

The calculator also reports the smallest height that works with your width (and vice versa): the larger of the dimensional minimum and the required area divided by the other dimension. The sill — the bottom of the clear opening — may be no more than 44 inches above the finished floor. Where the sill is below ground, a window well must give at least 9 sq ft of floor area with at least 36 inches of width and projection, and wells deeper than 44 inches need a permanently fixed ladder or steps.