Egress Window Calculator

Check whether a basement or bedroom window opening meets IRC R310 minimum egress requirements for area, width, height, and sill height.

Floor type

Clear width (in)

Clear height (in)

Sill height above floor (in)

Result

Pass

A 24 in by 36 in opening at 30 in sill height meets all IRC R310 egress requirements

Quick Answer

An egress window calculator checks clear opening area, width, height, and sill height against IRC R310 minimums. A 24 by 36 inch opening at 30 inches sill height gives 6.0 square feet of clear area and passes all four requirements for a below-grade sleeping room or basement.

What An Egress Window Calculator Checks For Code Compliance

Basements and sleeping rooms need at least one opening that meets International Residential Code (IRC) Section R310 minimums for emergency escape and rescue. The check covers four separate minimums: net clear opening area of at least 5.7 square feet (5.0 square feet for grade-floor openings), minimum clear width of 20 inches, minimum clear height of 24 inches, and maximum sill height of 44 inches above the finished floor. All four must pass for the opening to meet code. This tool checks the numeric minimums only; local jurisdictions may have additional amendments, so always confirm with the local building department before finalizing a window selection.

How IRC R310 Egress Minimums Are Checked

Net clear area (sq ft) = (clear width in × clear height in) ÷ 144. Passes when area ≥ 5.7 sq ft (5.0 for grade-floor), width ≥ 20 in, height ≥ 24 in, and sill height ≤ 44 in.

Net clear area = (clear width in inches × clear height in inches) ÷ 144.
Minimum area: 5.7 sq ft standard, or 5.0 sq ft for grade-floor openings.
Minimum clear width: 20 inches.
Minimum clear height: 24 inches.
Maximum sill height above floor: 44 inches.

Using This Egress Window Calculator In Four Steps

Inputs

Floor type: below grade (basement/upper floor) or grade floor (ground level).
Clear width: the net unobstructed width when the window is fully open, in inches.
Clear height: the net unobstructed height when the window is fully open, in inches.
Sill height: height of the window bottom above the finished floor, in inches.

Steps

Choose below grade or grade floor.
Measure and enter the clear (net) width in inches.
Measure and enter the clear (net) height in inches.
Measure and enter the sill height above the finished floor.
Read the pass/fail result and which specific requirements were checked.

Egress Window Example With Each Check Shown

Below-grade opening, 24 in clear width, 36 in clear height, 30 in sill height.

Net clear area: (24 × 36) ÷ 144 = 6.0 sq ft.
Area check: 6.0 sq ft ≥ 5.7 sq ft, pass.
Width check: 24 in ≥ 20 in, pass.
Height check: 36 in ≥ 24 in, pass.
Sill height check: 30 in ≤ 44 in, pass.

All four IRC R310 requirements pass for this below-grade opening.

When An Egress Window Check Fits A Basement Or Bedroom Project

Use this check when planning a basement bedroom, egress window well, or any sleeping room addition that requires a code-compliant emergency escape opening. Confirm the final window model's published net clear opening dimensions, not just its overall frame size, and check any local code amendments with the building department.

For nearby tools, the construction calculators hub lists every framing and code-check calculator, and the glossary defines common calculator terms.

Assumptions

Dimensions entered are net clear opening, not rough opening or frame size.
IRC R310 minimums are used as published in the base code.
No local code amendments are applied.

Limitations

Local jurisdictions may adopt stricter or different egress amendments.
Window well dimensions and ladder requirements for below-grade wells are not checked here.
The tool does not verify manufacturer-published net clear opening specs.
This is a planning check, not a substitute for building department approval.

In Practice

A common mistake is measuring the window frame or rough opening instead of the net clear opening, which is the actual unobstructed space someone can climb through when the window is fully open. Always measure the clear opening with the window in its fully open position, not the frame size.

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Frequently Asked Questions About Egress Window Requirements

What Is The Minimum Egress Window Opening Size?

IRC R310 requires a minimum net clear opening area of 5.7 square feet (5.0 square feet for grade-floor openings), with minimum clear width of 20 inches and minimum clear height of 24 inches, whichever combination reaches the area minimum.

What Is The Maximum Sill Height For An Egress Window?

The maximum sill height above the finished floor is 44 inches. A window with a sill higher than that does not meet egress requirements even if the opening area and dimensions otherwise pass.

Is Clear Opening The Same As Window Size?

No, clear opening is the net unobstructed space when the window is fully open, which is smaller than the overall frame or rough opening size. Always use the manufacturer's published net clear opening dimensions.

Does A Basement Always Need An Egress Window?

Any basement with a habitable space or sleeping room typically requires at least one egress-compliant opening under IRC R310. Confirm the exact requirement and any local amendments with the building department before finalizing plans.

Sources

Last updated: July 21, 2026. Reviewed for accuracy against the formula shown above.