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Code checker

Egress Window Calculator

Check a basement or bedroom window against the International Residential Code: clear opening area, height, width, sill height, the window well and whether it needs a ladder. Every result shows your number, the minimum, and the code section behind it.

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Use the result wisely

What this checks

  • Net clear opening, clear height and clear width — only the part that opens.
  • Floor-to-opening height, and the 5 sq ft grade-floor exception.
  • Window well area, width, projection, and when a ladder is required.
  • A measured opening, or a listed size with the frame allowance worked out.

Based on the 2024 IRC (Section R319). Not a code-compliance determination — your building department decides, and local amendments differ.

The short answer

An egress window needs a net clear opening of at least 5.7 sq ft (5 sq ft when the bottom of the opening is within 44 in of the outside ground), at least 24 in of clear height and 20 in of clear width, and the bottom of the opening no more than 44 in above the floor. It must open from inside without keys or tools. Below grade it needs a window well at least 9 sq ft, 36 in wide and 36 in out from the wall, with a permanent ladder or steps if the well is deeper than 44 in.

Source: 2024 International Residential Code, Section R319 (numbered R310 in the 2021 and 2018 editions, with the same numbers). Meeting 20 in and 24 in is not enough on its own: a 20 × 24 in opening is only 3.33 sq ft.

Egress checker

Check the window against each rule

Enter the opening, the sill height and the window well. Every result shows your number, the code minimum, and the section it comes from.

Only the panel that slides open counts — roughly half the window's width, minus the frame and the overlapping sash.

Required. Every sleeping room needs its own escape opening, including each bedroom in a basement (R319.1). The main exception is a home with an automatic sprinkler system where the basement also has a second way out.

What numbers do you have?

Open the window fully by normal operation. Measure the clear, unobstructed width and height at the narrowest points — inside the frame, stops and any sash or hardware that stays in the opening.

in

Clear width with the window fully open.

in

Clear height with the window fully open.

in

From the finished floor inside up to the bottom of the clear opening — not to the trim or the top of the sill.

in

Within 44 in of the outside ground, the minimum area drops to 5 sq ft.

in

Top of the well down to its floor.

in

Measured along the house wall.

in

How far it sticks out from the wall.

Code edition

The numbers are the same in all three editions. The difference: under 2018, every below-grade opening gets the 5 sq ft minimum; since 2021 only openings within 44 in of outside ground do. Your state or town may use an older edition or amend it — your building department can tell you which.

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How the rules fit together

What an egress window actually has to do

An emergency escape and rescue opening — the code's name for an egress window — has two jobs: let someone climb out of a room they can't leave through the door, and let a rescuer climb in. Every number follows from that: the 44 in sill limit is about reaching the opening, and the 5.7 sq ft area, 24 in height and 20 in width are about fitting a person through it.

The single most common mistake is measuring the wrong thing. The code counts only the net clear opening you get by opening the window normally. On a slider, that is one panel; on a single- or double-hung, one sash. A “48 × 36 window” is a frame size, and its clear opening can be half of it or less.

The second most common mistake is the window well. A basement egress window whose bottom is below the ground outside needs a well big enough to stand in and climb out of — at least 9 sq ft, 36 in wide and 36 in out from the wall — with a ladder once it is more than 44 in deep. A well that fills with water is a leak waiting to happen, which is why the code also requires it to drain.

Egress window, sill height and window wellCross-section of a basement egress window. Inside, the bottom of the clear opening is no more than 44 inches above the basement floor. Outside, the window opens into a window well dug below the ground. The well projects at least 36 inches out from the foundation wall, and a well deeper than 44 inches needs a permanent ladder, drawn here as rungs on the well's outer wall.ground≤ 44 infloor to bottomof openingclear height≥ 24 inprojection ≥ 36 inwidth ≥ 36 in, area ≥ 9 sq ftladderdepth > 44 in → ladderbasement
Inside, the bottom of the clear opening must be 44 in or less above the floor. Outside, the well must project at least 36 in and needs a ladder once it is deeper than 44 in.

Only the part that opens counts

Slider, casement, hung or awning?

Only the operable sash countsFront view of two windows. On a horizontal slider only the panel that slides open counts toward the clear opening, about half the width. On a single- or double-hung window only the lower sash opening counts, about half the height. The clear opening must be at least 20 inches wide, 24 inches high and 5.7 square feet.openfixedSlider≥ 20 inupper sashopenSingle/double-hung≥ 24 inShaded area ≥ 5.7 sq ft (5 sq ft grade-floor)
A slider opens about half its width and a hung window about half its height. Only the shaded opening counts toward the 5.7 sq ft.
  • Casement. The best egress window for its size, because the whole sash swings out. In a window well, the open sash needs room — the code says the well must let the window open fully.
  • Horizontal slider. The usual choice in wide, short basement openings. Only the sliding panel counts, so half the unit width has to exceed 20 in with the frame and overlapping sash taken off — a unit well over 40 in wide.
  • Single- or double-hung. Only one sash opens, so half the unit height has to exceed 24 in after the frame and meeting rail — a unit well over 48 in tall. A double-hung doesn't double the opening.
  • Awning or hopper. The gap under a tilted sash is rarely enough, and the size depends on how far it swings. Few are rated for egress; measure the real opening or check the rating.

Common sizes

Which window sizes can meet egress?

Common listed sizes, run through the same functions as the calculator. These are not manufacturer specifications — they show the most each window could possibly open, and how much the frame and sash can take away before it fails.

Listed sizeTypePart that opens (best case)Best-case areaCan it meet egress?
24 × 36 inCasement24 × 36 in6 sq ftEffectively no — needs a frame under 0.7 in
24 × 48 inCasement24 × 48 in8 sq ftTight — passes only if the frame takes ≤ 4 in
30 × 48 inCasement30 × 48 in10 sq ftRoom to spare — passes if the frame takes ≤ 9 in
36 × 36 inCasement36 × 36 in9 sq ftRoom to spare — passes if the frame takes ≤ 7.4 in
36 × 36 inSlider18 × 36 in4.5 sq ftCan't pass
48 × 36 inSlider24 × 36 in6 sq ftEffectively no — needs a frame under 0.7 in
48 × 48 inSlider24 × 48 in8 sq ftTight — passes only if the frame takes ≤ 4 in
60 × 36 inSlider30 × 36 in7.5 sq ftTight — passes only if the frame takes ≤ 4.2 in
60 × 48 inSlider30 × 48 in10 sq ftRoom to spare — passes if the frame takes ≤ 9 in
36 × 48 inSingle/double-hung36 × 24 in6 sq ftNo — the open half is right at the minimum before any frame
36 × 60 inSingle/double-hung36 × 30 in7.5 sq ftTight — passes only if the frame takes ≤ 4.2 in
48 × 48 inSingle/double-hung48 × 24 in8 sq ftNo — the open half is right at the minimum before any frame
36 × 72 inSingle/double-hung36 × 36 in9 sq ftRoom to spare — passes if the frame takes ≤ 7.4 in

Unit sizes are width × height in inches. Checked against the 5.7 sq ft minimum; a grade-floor opening needs only 5 sq ft, which loosens every row.

How to measure

Get numbers the inspector will agree with

  1. Open the window fully, the normal way — no removing sashes or popping out panels.
  2. Measure the clear width at the narrowest point between the frame, stops and any sash or hardware still in the opening.
  3. Measure the clear height the same way, from the bottom of the opening to the top.
  4. Multiply width × height in inches and divide by 144 for square feet. 5.7 sq ft is 820.8 sq in.
  5. Measure from the finished floor to the bottom of the clear opening — not to the trim or the top of the sill.
  6. Outside, measure the well's width along the wall, how far it projects from the wall, and its depth from the top of the well to its floor.

The rules, cited

Egress window requirements in the code text

Each rule the calculator checks, with the code's own words. Section numbers are from the 2024 International Residential Code, with the 2021 numbers in brackets.

IRC R319.2.1 (2021: R310.2.1)

Minimum net clear opening area

≥ 5.7 sq ft net clear opening; 5 sq ft for a grade-floor opening

“Emergency escape and rescue openings shall have a net clear opening of not less than 5.7 square feet (0.530 m2). Exception: The minimum net clear opening for grade-floor emergency escape and rescue openings shall be 5 square feet (0.465 m2).”

The 2018 IRC exception read "Grade floor openings or below-grade openings shall have a net clear opening area of not less than 5 square feet", so under 2018 every below-grade opening qualified for 5 sq ft.

IRC Chapter 2 definition

What counts as a grade-floor opening

Grade floor = bottom of the opening within 44 in above or below outside ground

“GRADE FLOOR EMERGENCY ESCAPE AND RESCUE OPENING. An emergency escape and rescue opening located such that the bottom of the clear opening is not more than 44 inches (1118 mm) above or below the finished ground level adjacent to the opening.”

IRC R319.2.2 (2021: R310.2.2)

Minimum clear height and width

Clear height ≥ 24 in and clear width ≥ 20 in, by normal operation

“The minimum net clear opening height dimension shall be 24 inches (610 mm). The minimum net clear opening width dimension shall be 20 inches (508 mm). The net clear opening dimensions shall be the result of normal operation of the opening.”

IRC R319.2.3 (2021: R310.2.3)

Maximum height from the floor

Bottom of the clear opening ≤ 44 in above the floor

“Emergency escape and rescue openings shall have the bottom of the clear opening not greater than 44 inches (1118 mm) above the floor.”

The 2018 IRC (R310.2.2) said a window "shall have a sill height of not more than 44 inches (1118 mm) above the floor". Since 2021 the measurement is to the bottom of the clear opening, not the sill trim.

IRC R319.1.1 (2021: R310.1.1)

Opens without keys, tools or special knowledge

Opens from inside without keys, tools or special knowledge

“Emergency escape and rescue openings shall be operational from the inside of the room without the use of keys, tools or special knowledge.”

Window opening control devices and fall prevention devices complying with ASTM F2090 are permitted, mounted not more than 70 inches above the finished floor.

IRC R319.4 (2021: R310.4)

When a window well is required

A well is required when the bottom of the opening is below the ground outside

“An emergency escape and rescue opening where the bottom of the clear opening is below the adjacent grade shall be provided with an area well in accordance with Sections R319.4.1 through R319.4.4.”

IRC R319.4.1 (2021: R310.4.1)

Minimum window well size

Well ≥ 9 sq ft, with width and projection each ≥ 36 in; the window must open fully

“The horizontal area of the area well shall be not less than 9 square feet (0.9 m2), with a horizontal projection and width of not less than 36 inches (914 mm). The size of the area well shall allow the emergency escape and rescue opening to be fully opened.”

Exception: the required ladder or steps may encroach not more than 6 inches into the required dimensions of the well.

IRC R319.4.2 (2021: R310.4.2)

Ladder or steps in deep wells

Wells deeper than 44 in need a permanently affixed ladder or steps

“Area wells with a vertical depth greater than 44 inches (1118 mm) shall be equipped with an approved, permanently affixed ladder or steps. The ladder or steps shall not be obstructed by the emergency escape and rescue opening where the window or door is in the open position.”

IRC R319.4.2.1 (2021: R310.4.2.1)

Ladder rungs

Rungs ≥ 12 in wide inside, ≥ 3 in off the wall, ≤ 18 in apart

“Ladders and rungs shall have an inside width of not less than 12 inches (305 mm), shall project not less than 3 inches (76 mm) from the wall and shall be spaced not more than 18 inches (457 mm) on center vertically for the full height of the area well.”

IRC R319.4.3 (2021: R310.4.3)

Window well drainage

Well drains to the foundation drainage system (unless on Group I soils)

“Area wells shall be designed for proper drainage by connecting to the building’s foundation drainage system required by Section R405.1.”

Exception: no drainage system is required where the foundation is on well-drained soil or sand-gravel mixture soils (Group I soils).

IRC R319.4.4 (2021: R310.4.4)

Bars, grilles, covers and screens

Covers, bars and grilles release from inside without a key, tool or extra force

“Such devices shall be releasable or removable from the inside without the use of a key or tool or force greater than that required for the normal operation of the escape and rescue opening.”

IRC R319.2.4 (2021: R310.2.4)

Openings under decks, porches and cantilevers

Under a deck or porch: fully openable, with a 36 × 36 in path out

“Emergency escape and rescue openings installed under decks, porches and cantilevers shall be fully openable and provide a path not less than 36 inches (914 mm) in height and 36 inches (914 mm) in width to a yard or court.”

The 2018 IRC required a path 36 inches in height only, and did not mention cantilevers.

IRC R319.1 (2021: R310.1)

Where an egress opening is required

Required in basements and every sleeping room (with listed exceptions)

“Basements, habitable attics, the room to which a sleeping loft is open, and every sleeping room shall have not less than one operable emergency escape and rescue opening. Where basements contain one or more sleeping rooms, an emergency escape and rescue opening shall be required in each sleeping room.”

Exceptions include basements used only to house mechanical equipment and not over 200 sq ft, storm shelters built to ICC 500, and basement sleeping rooms in a home with an automatic sprinkler system where the basement has the required second way out. The 2024 edition added "the room to which a sleeping loft is open".

IRC R319.7 (2021: R310.7)

Remodeling an existing basement

Finishing an existing basement triggers one only for a new bedroom

“New sleeping rooms created in an existing basement shall be provided with emergency escape and rescue openings in accordance with Section R319.1. Other than new sleeping rooms, where existing basements undergo alterations or repairs, an emergency escape and rescue opening is not required.”

IRC R319.5 (2021: R310.5)

Replacement windows

A replacement window can be exempt from the size rules

“The replacement window is the manufacturer’s largest standard size window that will fit within the existing frame or existing rough opening.”

A replacement window meeting this condition (and not part of a change of occupancy) is exempt from the size rules of R319.2 and the cover rule of R319.4.4. It may keep the same operating style, or use a style with an equal or greater opening.

Before you cut the wall

An egress window is also a new way for water to get in

A new egress window turns a small basement window into a large opening at the bottom of a hole in the ground. If the well can't drain, rain and roof water fill it above the sill. That is why the code requires area wells to connect to the foundation drainage system, and why most leaking basement windows turn out to be a well problem, not a window problem. Our window well drain guide covers how to size and test the drain.

If water already comes through the wall near the window, sort out the source first with the water source diagnostic or the guide to water coming through a basement wall. Finishing the space afterward? Run the basement waterproofing checklist first.

FAQs

Egress window questions

What is the minimum requirement for an egress window?

Under the 2024 International Residential Code (Section R319, the same numbers as R310 in 2021 and 2018): a net clear opening of at least 5.7 sq ft, or 5 sq ft for a grade-floor opening; a clear height of at least 24 in and a clear width of at least 20 in; the bottom of the opening no more than 44 in above the floor; and it must open from inside without keys, tools or special knowledge. A below-grade egress window also needs a window well of at least 9 sq ft with 36 in of width and projection, plus a permanent ladder or steps if the well is deeper than 44 in.

Does a 36x36 casement window meet egress?

It can. A casement opens the whole sash, so a 36 × 36 in unit has up to 36 × 36 in (9 sq ft) to work with. It still passes if the frame, sash and hinges take no more than about 7.4 in off each dimension, leaving a clear opening of at least 28.6 × 28.6 in. Hinge and crank hardware can narrow the clear width, so check the manufacturer's published net clear opening for that model.

Does a 3x5 single hung or double hung window meet egress?

It is borderline. A 3 × 5 ft (36 × 60 in) hung window only opens one sash, so the best case is about 36 × 30 in. The frame, meeting rail and sash can take no more than about 4.2 in off each dimension before it fails. For example, at 32 in of clear width it needs 25.7 in of clear height; a 32 × 25 in clear opening is only 5.56 sq ft. Check the exact model's net clear opening.

Does a 48x36 window meet egress?

As a slider (48 in wide, 36 in tall), almost never: only the sliding panel opens, so the best case is 24 × 36 in, and the frame could take away no more than about 0.7 in before it drops below 5.7 sq ft. As a hung window it can't, because opening half of 36 in gives less than the 24 in minimum height. A casement or a taller slider is the usual fix.

Does a 4x4 window meet egress?

A 48 × 48 in slider can: its sliding panel gives up to 24 × 48 in, and the limit is the 20 in width — the frame and sash can take about 4 in off the panel width. A 48 × 48 in hung window effectively can't, because half the height is exactly 24 in before any frame is subtracted.

Do all bedrooms have to have an egress window?

Under the IRC, every sleeping room needs at least one emergency escape and rescue opening (R319.1), and each bedroom in a basement needs its own. The opening can be a window, or a side-hinged or sliding door to the outside (R319.3). The main exception is a basement bedroom in a home with an automatic sprinkler system where the basement also has the required second way out.

Is it illegal to sleep in a basement without an egress window?

The IRC governs how rooms are built and permitted rather than where someone sleeps. A basement room built or permitted as a bedroom must have an escape opening, and creating a new bedroom in an existing basement triggers one (R319.7). Rental housing codes and local ordinances can add their own rules, so check with your building department. Whatever the code, a basement bedroom without a second way out is a real fire risk.

Can you finish a basement without an egress window?

Under the model IRC, often yes if you don't add a bedroom. R319.7 says new sleeping rooms in an existing basement need escape openings, but other alterations or repairs of an existing basement do not. New basements, including basements in additions, need at least one (R319.1 and R319.6). Many towns amend this, so confirm before you finish the space.

Can I install my own egress window?

Many homeowners do part of the work, but cutting a larger opening in a foundation wall usually needs a permit and often a structural header, and the well needs drainage to the foundation drain (R319.4.3). Ask your building department what it requires, and have anyone cutting concrete check for utilities first.

Does a replacement window have to meet egress size?

Not always. Under R319.5, a replacement for an existing escape window is exempt from the size rules if it is the manufacturer's largest standard size that fits the existing frame or rough opening, is the same operating style or one that opens as much or more, and is not part of a change of occupancy. It must still open without keys or tools.

Can a window well have a cover over an egress window?

Yes, but it must be releasable or removable from inside without a key, a tool or more force than it takes to open the window (R319.4.4), and it can't reduce the required clear opening or the well size.

Related pages

Where to go next

Window well drain

Why wells fill and leak, and how to drain one to code.

Read next

Water coming through a basement wall

Trace a wall leak before cutting a new opening.

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Basement waterproofing checklist

What to settle before you finish a basement.

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Basement flood risk score

Window wells, grading and sump reliability in one score.

Read next

Methodology

How this calculator works

The calculator uses the 2024 International Residential Code, Section R319, read from the ICC's free public-access text on September 27, 2026. The 2021 IRC (Section R310) has the same numbers, and so does the 2018 IRC, with two differences the calculator handles: under 2018, every below-grade opening gets the 5 sq ft minimum, and the limit is written as the window's sill height rather than the bottom of the clear opening.

States and towns adopt different editions, sometimes years behind, and amend them. North Carolina, for example, publishes its own state residential code based on an IRC edition. Your building department decides which rules apply and whether a window complies.

Area is width × height of the clear opening in square inches ÷ 144. For a listed size, the calculator assumes the best case for the part that opens and solves for the most the frame can take off each dimension. Nothing is stored and no manufacturer data is used.

Not a code-compliance determination. This is a planning check against the model code. Your building department decides.

Last updated: September 27, 2026. Code text checked: 2026-09-27.

Sources