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Framing & structure · Egress Window Size Checker

Is a 20 x 24 clear opening big enough for egress?

A clear opening 20 in wide by 24 in high is 3.33 sq ft. That is under the minimum area, even though the width and the height each meet their own minimum. These are clear opening sizes, not the size on the window label: measure yours and enter it below.

Short answer
Net clear opening area (20 in × 24 in)
3.33 sq ft
Against the 5.7 sq ft minimum
Fails, 340.8 sq in short
Against the 5 sq ft minimum for a grade-floor opening
Fails, 240 sq in short
Clear height needed at 20 in wide for 5.7 sq ft
41 1/16 in
Clear width needed at 24 in high for 5.7 sq ft
34 1/4 in
20 x 24 here is the clear opening, not the size a window is sold by
measure yours

2021 IRC Section R310. Width first, then height, both measured as the free opening with the window opened the normal way. This tool applies the 5 sq ft minimum only where the bottom of the opening is at or above the ground outside and no more than 44 in above it. An opening below the ground is held to 5.7 sq ft and must also have a window well. The bottom of the opening must be no more than 44 in above the floor.

Your window
in
in

Open the window the normal way and measure the free hole you could climb through, between whatever is still in the way (sash, frame, stops, hardware). Not the frame size and not the size on the label. Inches with fractions, like 20 1/2. Replace the starting numbers with yours. The code's minimum width and minimum height fail together.

in
Inside the room, from the finished floor straight up to the lowest edge of the open hole. The limit is 44 in. Inches: for 3 ft 4 in type 40 or 3' 4".
Is the bottom of the clear opening below the ground outside?

The ground means the finished surface of the yard beside the house. If there is a window well in front of this window, the answer is Yes: the floor of a well is not the ground.

Result
Not checkedEnter your measurements to see a result.

    Areas are rounded down to 0.01 sq ft. Required dimensions are rounded up, to the next 1/16 in and to the next 0.01 in. Your own measurements are shown as typed. 2021 IRC Section R310.

    The wall seen from inside the room, drawn to scale. The dashed line is the 44 in limit for the bottom of the opening.

    Rule: 2021 IRC R310 · Tested against 29 worked examples, 9 printed in a published source · How this is worked out →

    Questions people ask

    What is the minimum size for an egress window?
    Under 2021 IRC R310 the net clear opening must be at least 5.7 square feet, at least 24 inches high and at least 20 inches wide, with the bottom of the clear opening no more than 44 inches above the floor. For a grade-floor opening, which the code defines as one whose bottom is within 44 inches above or below the finished ground next to it, the minimum area is 5 square feet. This tool applies the 5 sq ft minimum only where the bottom of the opening is at or above the ground outside and no more than 44 in above it. An opening below the ground is held to 5.7 sq ft and must also have a window well.
    Is a window 20 inches wide and 24 inches high big enough for egress?
    No. Those are the minimum width and the minimum height, but together they give only 3.33 sq ft, well under 5.7. At 20 inches wide the clear opening has to be 41.04 inches high (41 1/16 on a tape) to reach 5.7 square feet, or 36 inches for the 5 square foot grade-floor minimum. At 24 inches high it has to be 34.2 inches wide.
    What does net clear opening mean?
    The code says the net clear opening dimensions are the result of normal operation of the opening, and that the opening must work from inside the room without keys, tools or special knowledge. It gives no further definition. This tool takes it as the free space left when the window is opened the normal way, measured between whatever still blocks the hole. That is not the same as the frame size or the size on the label.
    How high can an egress window be off the floor?
    The bottom of the clear opening can be no more than 44 inches above the floor. The 2021 text measures to the bottom of the clear opening; the 2018 text states the same limit as a sill height.
    What size does an egress window well have to be?
    Where the bottom of the clear opening is below the ground outside, the 2021 code requires an area well with a horizontal area of at least 9 square feet and at least 36 inches in both width and projection from the wall, sized so the window can open fully. A well with a vertical depth of more than 44 inches needs a permanently fixed ladder or steps, which may project up to 6 inches into those dimensions. The code does not say where the depth is measured from, or how the width and projection apply to a curved well.