Egress Window Size Calculator

The egress window size calculator checks a bedroom window's net clear opening against four IRC R310 requirements: 5.7 sq ft of area (5.0 sq ft at grade), 20 in. width, 24 in. height and a sill no higher than 44 in. It returns the net clear area and whether the opening passes all four.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Net Clear Opening Area

6.00 sq ft

IRC R310 Compliance Check

This opening meets IRC R310's egress requirements (6.00 sq ft net clear area).

Breakdown
Net Clear Opening Area	6.00 sq ft

How to Calculate Egress Window Size

The IRC requires every sleeping room (and most basements) to have at least one emergency escape and rescue opening. That opening must meet four separate minimums at once. The net clear opening area must be at least 5.7 sq ft. For a grade-floor opening, the relaxed minimum is 5.0 sq ft, since less climbing distance is involved. The clear width must be at least 20 in., the clear height at least 24 in., and the sill no higher than 44 in. above the finished floor. A window can fail egress even with plenty of total area if its width or height alone falls under the minimum. A tall, narrow window and a short, wide window can have the same area, but only one of them may actually meet all four checks.

Example: 24 in. wide × 36 in. tall opening, 40 in. sill height

A 24 in. wide × 36 in. tall opening, 40 in. sill height, not a grade-floor opening: 1. Net clear area: (24 × 36) ÷ 144 = 864 ÷ 144 = 6.0 sq ft (clears the 5.7 sq ft minimum). 2. Width: 24 in. (clears the 20 in. minimum). 3. Height: 36 in. (clears the 24 in. minimum). 4. Sill height: 40 in. (under the 44 in. maximum). This opening passes all four IRC R310 checks.

What Is Egress Window Size?

An egress window calculator checks a bedroom (or basement) window opening's net clear dimensions against all four of the IRC's emergency escape and rescue opening requirements at once. It is a real safety code check for anyone planning a new bedroom, a basement bedroom conversion, or a window replacement in an existing sleeping room.

Egress Window Size: Pros and Cons

Pros

Checks all four IRC minimums at once (area, width, height, sill height), catching a failure that a single-number area check alone would miss
Applies the correct, relaxed 5.0 sq ft area minimum for grade-floor openings automatically
A useful pre-check before ordering a window or planning a bedroom/basement conversion

Cons

"Net clear opening" means the actual openable space, accounting for the sash, screen frame, and any window well or grille. It is not the window unit's rough opening or overall frame size. Measure the actual clear opening, not the window's nominal size
A below-grade window well (for a basement egress window) has its own separate IRC requirements (minimum area, projection, and a permanently affixed ladder if deep enough) not checked by this calculator
Always confirm with your local building department, since some jurisdictions adopt amendments to these baseline IRC figures

Egress Window Size: What a Pro Checks

Measure the net clear opening, not the window unit's rough opening or overall frame size. The actual openable space is smaller once you exclude the sash and screen frame, and that's the figure IRC R310 checks.
A below-grade window well has its own separate requirements (minimum area, projection, and a permanent ladder if deep enough) beyond the window opening itself. Check those separately for a basement egress window.
Confirm the exact figures with your local building department before finalizing a window order. Some jurisdictions adopt amendments to these baseline IRC R310 numbers.

Frequently Asked Questions

What is the minimum size for an egress window?

A net clear opening area of at least 5.7 sq ft (5.0 sq ft for a grade-floor opening), with a minimum clear width of 20 in. and a minimum clear height of 24 in. All four must be met at once. Total area alone doesn't pass.

How high can an egress window sill be?

No more than 44 in. above the finished floor, per IRC R310.2.3. A higher sill fails the requirement regardless of the window's size, since it needs to be reachable for emergency escape.

Does a basement need an egress window?

Yes, in most jurisdictions. The IRC requires an egress opening in habitable basement spaces and any basement with a sleeping room. It follows the same size, width, height, and sill requirements as an upper-floor bedroom. The relaxed 5.0 sq ft area minimum applies if the basement window is at or near grade.

What is net clear opening vs. rough opening?

Net clear opening is the actual space a person can physically pass through once the window is open. It is smaller than the window unit's overall rough opening or frame size, since it excludes the sash, screen frame, and any obstruction. Always measure the true clear opening for an egress check, not the window's nominal size.

Does every bedroom window need to meet egress requirements?

The IRC requires at least one egress-compliant opening per sleeping room. It doesn't require every window in the room to qualify. Other windows in the same bedroom don't need to individually meet the egress minimums as long as one does.

Sources

2021 International Residential Code, Section R310.2 (Emergency Escape and Rescue Openings): minimum size, dimensions, and sill height (opens in a new tab)

Electrical