Egress Window Calculator
Will your window pass egress? This free egress window calculator checks a bedroom or basement window against the IRC R310 emergency escape and rescue (EERO) requirements: the net clear opening area, the minimum opening height and width, and the maximum sill height above the floor. Enter the opening and get an instant pass or fail.
The number that trips people up is the net clear opening — the actual free space with the sash fully open, not the rough opening, the nominal window size, or the glass size. Because a 20-inch by 24-inch opening is only 3.33 square feet, you can never meet the 5.7 square foot minimum at both minimum dimensions; the calculator solves for the height or width you actually need.
Requirements come straight from IRC R310 (unchanged in value across the 2015, 2018, 2021, and 2024 editions), with built-in handling for the grade-floor and below-grade 5.0 square foot exception, window-well rules, and jurisdiction outliers like New York City's 6.0 square foot minimum and the Massachusetts hung-window relaxation. Always confirm the code edition your local building department has adopted.
Egress Window Calculator
Check whether a bedroom or basement window meets the IRC R310 emergency escape & rescue requirements — net clear opening area, minimum height and width, and maximum sill height. Free, no signup.
Window & opening
Enter the NET CLEAR opening — the actual free space with the sash fully open, not the rough or nominal window size.
Grade-floor and below-grade openings qualify for the reduced 5.0 sq ft minimum; all other openings need 5.7 sq ft (6.0 sq ft in NYC).
Calculation Formulas
The net clear opening is the actual free passage with the sash fully open in normal operation — NOT the rough opening, nominal/called size, or glass size. This is the single most common reason a window fails egress inspection.
Example:
A 32" × 28" net clear opening = 896 sq in = 6.22 sq ft — meets the 5.7 sq ft minimum.
IRC R310.2.1 requires a 5.7 sq ft minimum net clear opening, reduced to 5.0 sq ft for grade-floor and below-grade openings. NYC is a genuine outlier at 6.0 sq ft.
Example:
20" × 24" = 480 sq in = 3.33 sq ft — fails 5.7 sq ft despite meeting both minimum dimensions.
Because 20 × 24 is only 3.33 sq ft, at least one dimension must exceed its minimum. At the 20" minimum width you need ≥ 41.04" height; at the 24" minimum height you need ≥ 34.2" width.
Example:
To reach 5.7 sq ft with a 24"-tall opening: 820.8 ÷ 24 = 34.2" minimum width.
When the area fails, the calculator solves for the smaller dimension needed at the existing width or height so you can spec a compliant unit.
Example:
At 30" width for 5.0 sq ft below grade: 720 ÷ 30 = 24" minimum height.
IRC R310.2.1 sets independent floor dimensions in addition to the area — both must be met regardless of total area.
Example:
A 40" × 18" opening is 5.0 sq ft but fails the 20" minimum width.
IRC R310.2.2 caps the sill at 44 in above the finished floor so an occupant can reach and climb through. A permanent step or landing can lower the effective sill.
Example:
A sill 48" above the floor fails; adding a permanent 6" landing brings it to 42".
IRC R310.4 requires below-grade openings to sit in an area well at least 9 sq ft with 36 in of projection and width, and the window must fully open into it.
Example:
A 36" × 40" well = 10 sq ft — meets the 9 sq ft minimum.
IRC R310.4.2: wells deeper than 44 in need a permanent ladder or steps (rungs ≥ 12" wide, ≥ 3" projection, ≤ 18" on center; may encroach up to 6" into the well).
Example:
A 50"-deep well requires a fixed ladder; a 42"-deep well does not.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Minimum net clear opening area | 5.7 sq ft (820.8 sq in) | IRC R310.2.1 — standard requirement for sleeping-room and basement EEROs. |
| Grade-floor / below-grade area | 5.0 sq ft (720 sq in) | Reduced minimum for openings at or below grade (IRC R310.2.1 exception). |
| NYC minimum area | 6.0 sq ft (864 sq in) | NYC Building Code §BC 1030.2 — a genuine outlier; NYC does not use the IRC. |
| Massachusetts hung-window minimum | 3.3 sq ft (475.2 sq in) | 780 CMR relaxation for single- and double-hung units only; other types keep 5.7 sq ft. |
| Minimum net clear height | 24 in | IRC R310.2.1 — independent of area. |
| Minimum net clear width | 20 in | IRC R310.2.1 — independent of area. |
| Maximum sill height | 44 in above finished floor | IRC R310.2.2 — measured to the bottom of the clear opening. |
| Minimum window-well area | 9 sq ft | IRC R310.4.1 — with 36 in minimum projection and width. |
| Window-well ladder trigger depth | over 44 in | IRC R310.4.2 — deeper wells require a permanent ladder or steps. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
IRC R310 — Emergency Escape and Rescue Openings(IRC R310.2.1 / R310.2.2 / R310.4)
View StandardThe model residential code adopted (with amendments) by most US states. The four core dimensions — 5.7 sq ft net clear area (5.0 sq ft grade-floor/below-grade), 24 in minimum height, 20 in minimum width, 44 in maximum sill — are unchanged in value across the 2015, 2018, 2021, and 2024 editions; only the section numbering changed.
Key Requirements:
- •Every sleeping room and every basement (with limited exceptions) needs a compliant emergency escape and rescue opening.
- •Net clear opening ≥ 5.7 sq ft (5.0 sq ft for grade-floor and below-grade openings).
- •Minimum net clear opening height 24 in and width 20 in — both required in addition to the area.
- •Sill no more than 44 in above the finished floor; opening operable from inside without keys, tools, or special knowledge.
IRC R310.4 — Area (Window) Wells(IRC R310.4.1 / R310.4.2)
View StandardRequirements for the well serving a below-grade emergency opening. In IRC 2015/2018 these appear under "window wells" (R310.2.3); IRC 2021/2024 relocated them to R310.4 "area wells."
Key Requirements:
- •Minimum 9 sq ft horizontal floor area with 36 in minimum projection and width.
- •The emergency opening must be able to fully open into the well.
- •Wells deeper than 44 in require a permanent ladder or steps (rungs ≥ 12 in wide, ≥ 3 in projection, ≤ 18 in on center).
- •Drainage must connect to the foundation drainage system unless on well-drained Group I soils.
Replacement-window exemption(IRC 2018 R310.2.5 / IRC 2021 R310.5)
View StandardA like-for-like replacement window is exempt from the opening-area and sill-height requirements if it is the manufacturer’s largest standard size that fits the existing frame/rough opening, is the same operating style (or one with equal/greater opening), and is not part of a change of occupancy — the "you don’t have to enlarge the hole" allowance.
Key Requirements:
- •Replacement must be the largest standard size that fits the existing opening.
- •Same operating style, or one that provides an equal or greater clear opening.
- •Not applicable to a change of occupancy or new construction.
ASTM F2090 — Window fall-prevention & egress-release devices(ASTM F2090)
View StandardWindow opening control devices (WOCDs) and fall-prevention devices are permitted on emergency-escape windows only if they comply with ASTM F2090 and release from inside without keys, tools, or special knowledge, allowing the sash to open fully for escape.
Key Requirements:
- •Device limits the initial opening but releases to allow full egress.
- •Releasable from inside without keys, tools, or special knowledge.
- •Auto-resets on closing (per AAMA/WDMA TB-24-01).
IBC §1031 — Emergency Escape and Rescue (reference)(IBC §1031 (2021/2024))
View StandardThe commercial/multifamily counterpart. Dimensional numbers match the IRC, but the IBC applies outside detached one- and two-family dwellings and has occupancy-based exceptions (e.g., certain sprinklered or two-exit R-2 buildings).
Key Requirements:
- •Applies to R-2 and other occupancies outside the IRC scope.
- •Sprinkler and second-exit exceptions available per the Section 1006 exit tables.
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
New York City — larger minimum, not IRC
NYC Building Code §BC 1030 (2015-IBC based)
NYC does not use the IRC at all. Its emergency-opening minimum is 6.0 sq ft (5.0 sq ft grade-floor) — the calculator must not apply the 5.7 figure here. Most dwellings with a compliant second means of egress are exempt from the requirement entirely.
Regional Examples:
Massachusetts — single/double-hung relaxation
780 CMR R310.2.1 exception
Massachusetts allows a reduced 3.3 sq ft minimum net clear opening for single-hung and double-hung windows only, with a 20 in × 24 in minimum in either direction. Casements, sliders, and other types still meet the standard IRC 5.7 sq ft.
Regional Examples:
Minnesota — sprinkler waiver & licensed-care rooms
MN Rules 1309.0310
Minnesota waives the basement/basement-bedroom EERO where the dwelling is protected by an NFPA 13D or IRC P2904 sprinkler system — the model IRC does not grant this. Licensed foster/day-care sleeping rooms have stricter window rules (min 20 in × 20 in, 648 sq in clear opening, max 48 in sill).
Regional Examples:
Florida — impact-rated glazing in high-wind zones
FBC-Residential R310 + HVHZ §§1616–1626
Florida tracks the IRC R310 numbers, but in the High-Velocity Hurricane Zone (Miami-Dade and Broward) and the broader Wind-Borne Debris Region an egress window must simultaneously be impact-rated (Miami-Dade NOA in the HVHZ) and meet the net clear opening — which constrains the operable egress products available.
Regional Examples:
Code edition varies by state
IRC 2015 through IRC 2024
States adopt different IRC editions (2015–2024) with a 2–5 year lag after publication. The four core dimensions are the same across editions, so the pass/fail result is unchanged — only the section citation differs. Home-rule cities (e.g., Chicago) and states mid-adoption change frequently.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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How to Use This Calculator
- Pick the window type — casement, single- or double-hung, slider, awning, hopper, or fixed. The type affects how much of the unit becomes clear opening.
- Measure the net clear opening with the sash fully open and enter the width and height in inches — not the rough opening or the nominal window size.
- Enter the sill height above the finished floor, then choose whether the opening is upper-story, grade-floor, or below grade (the last two get the reduced 5.0 sq ft minimum).
- For a below-grade opening, add the window-well projection, width, and depth to check the 9 sq ft / 36-inch well and the 44-inch ladder trigger.
- Choose your jurisdiction if you are in NYC or Massachusetts, then click Check compliance for an instant pass/fail plus the exact dimension you need to reach if it fails.
- Confirm the adopted code edition and any local amendments with your building department before ordering a window.
Why "Net Clear Opening" Fails More Windows Than Any Other Rule
The single most common egress inspection failure is measuring the wrong thing. The code requirement is the net clear opening — the unobstructed space a person can actually pass through with the sash in its fully open, normal-operating position — which is smaller than the rough opening, the called/nominal window size, and the glass area. On a double-hung window only the lower sash counts, so the clear opening is roughly half the glazed height; on a slider only the moving panel counts. That is why a window advertised as a large unit can still fail. This calculator always works from the net clear opening you enter, so the result matches what an inspector measures — but verify against the manufacturer's published egress chart for your exact model rather than the nominal size.
Frequently Asked Questions
What size does an egress window need to be?
Under IRC R310, an emergency escape and rescue window needs a net clear opening of at least 5.7 square feet, a minimum opening height of 24 inches, a minimum opening width of 20 inches, and a sill no more than 44 inches above the finished floor. Grade-floor and below-grade openings get a reduced 5.0 square foot minimum. New York City is an outlier at 6.0 square feet.
Is the net clear opening the same as the window size?
No — and this is the most common reason windows fail egress inspection. The net clear opening is the actual free space a person can pass through with the sash fully open, not the rough opening, the nominal/called window size, or the glass area. On a double-hung window only the lower sash counts, so the clear opening is roughly half the glazed height. Always measure the opening or use the manufacturer's egress chart, not the nominal size.
Why can't a 20-inch by 24-inch window meet egress?
Because 20 inches by 24 inches is only 480 square inches, or 3.33 square feet — well short of the 5.7 square foot area minimum. You can never satisfy all four minimums at their floor values, so at least one dimension must be larger: at the 20-inch minimum width you need at least 41 inches of height, and at the 24-inch minimum height you need at least 34.2 inches of width.
Do basement bedrooms need an egress window?
Yes. IRC R310 requires an emergency escape and rescue opening in every sleeping room and in basements with habitable space. A basement bedroom needs its own compliant opening — a walkout door can satisfy the overall basement requirement, but each sleeping room still needs its own egress. Some states amend this; for example, Minnesota waives it for dwellings protected by a residential sprinkler system.
Does a below-grade egress window need a window well?
Yes. A below-grade opening needs an area well of at least 9 square feet with a minimum 36-inch projection and width, and the window must be able to fully open into it. If the well is deeper than 44 inches, a permanent ladder or steps is required. Wells must also drain to the foundation drainage system unless the soil is well-drained.
Can a double-hung or awning window be an egress window?
A double-hung window can qualify, but because only the lower sash opens, the unit has to be large — the clear opening is about half the glazed area. Casements are the most efficient and can reach 5.7 square feet in a smaller unit. Awning and hopper windows usually do NOT qualify because their hardware and sash angle limit the opening; verify against the manufacturer egress chart before specifying one.
Are egress window requirements different in my state?
The four core IRC R310 numbers are the same across the 2015, 2018, 2021, and 2024 editions, so most states match. The genuine outliers: New York City requires 6.0 square feet (and does not use the IRC at all), Massachusetts allows a reduced 3.3 square feet for single- and double-hung windows only, and Florida's high-wind zones add impact-rating requirements on top of R310. Always confirm the edition and amendments your local building department enforces.