A window well sizing calculator helps you meet IRC R310 egress code requirements for basement windows. Enter your window dimensions, well depth below grade, and well shape to get minimum well width, projection from the foundation wall, gravel volume needed, drainage requirements, whether a ladder or steps are required, and an estimated cover size.
Window & Well Dimensions
Distance from grade to well floor
IRC R310 Compliance Check
Full Specification
How to Use the Window Well Sizing Calculator
Basement egress windows must meet IRC R310 code requirements to be valid emergency exits. The window well surrounding an egress window must be large enough to allow the window to open fully and for a person to climb out. This window well sizing calculator checks your window dimensions against code minimums and outputs the full well specification.
Step 1: Enter Window Dimensions
Enter the rough opening width and height of the basement window in inches (or centimeters in metric mode). IRC R310 requires the window opening net clear area to be at least 5.7 sq ft, with a minimum clear opening width of 20 inches and minimum clear opening height of 24 inches. The window itself must be operable from the inside without a key, tool, or special knowledge.
Step 2: Set Well Depth and Shape
Enter the depth of the window well below finish grade — typically measured from grade level to the well floor. Choose rectangular (most common, easiest to install) or semi-circular (often used with prefab galvanized steel wells). The well must be deep enough to reach below the window sill plus provide clear space.
Step 3: Select Soil Type
Soil type determines drainage requirements. Sandy soils drain freely and a standard 6-inch gravel bed is usually sufficient. Clay soils require a drain tile or perforated pipe at the gravel layer connected to a drain, sump, or daylighted outlet. Without drainage in clay soil, window wells can fill with water and create hydrostatic pressure against the foundation.
Step 4: Review Code Compliance
The compliance check panel shows whether your window meets IRC R310 minimums. If anything is out of spec, the panel highlights what needs to change. If the well depth exceeds 44 inches, a permanently installed ladder or steps are required by code. The gravel volume estimate is based on your well plan dimensions with a 6-inch drainage bed.
Frequently Asked Questions
Is this window well sizing calculator free?
Yes, the window well sizing calculator is completely free with no usage limits. All calculations run locally in your browser — no signup, no account, and no data ever leaves your device.
Is my data private?
Yes, everything is calculated in your browser. Your window dimensions and project details are never sent to any server or stored remotely.
What are the IRC requirements for egress window wells?
IRC Section R310 requires that if a basement egress window well is more than 44 inches deep, it must have permanently installed ladder or steps. The well must allow the window to open fully and provide a minimum horizontal area. The opening itself must meet minimum net clear area (5.7 sq ft), width (20"), and height (24") requirements.
How wide does my window well need to be?
The minimum window well width is the rough opening width of the window plus 6 inches on each side (12 inches total), giving a minimum well width of at least 36 inches. Many jurisdictions and manufacturers require more — typically the window width plus 12 inches per side. Always check your local building department for amendments to the IRC.
How far does the window well need to project from the house?
The minimum horizontal projection (depth from house wall) must be at least 36 inches per IRC R310. This allows adequate space for a person to exit. If the window is wider than the minimum, some jurisdictions require additional projection. The well must also be large enough to allow the window to fully open.
How much gravel does a window well need?
A minimum 6-inch layer of gravel at the bottom of the window well is the standard drainage recommendation. Gravel allows water to drain away from the foundation wall and prevents the well from flooding. Connect the gravel to a perimeter drain or daylight drain if possible. The calculator estimates gravel volume based on well dimensions and a 6-inch gravel bed depth.
When do I need a window well cover?
Window well covers are recommended in all climates to keep out leaves, debris, snow, and animals. They must be removable from inside without tools so they do not impede emergency egress. Polycarbonate bubble covers are popular and allow natural light. A cover is often required by local codes, especially for wells deeper than 30 inches.