Window Well Size Calculator
Calculate the correct window well dimensions for basement egress windows based on building code requirements.
Window wells are excavated areas around basement windows that allow light and ventilation, and most importantly, provide emergency egress (escape). Building codes have strict minimum requirements for egress window wells to ensure occupants can safely exit during emergencies.
IRC (International Residential Code) Egress Requirements: Every bedroom in a basement must have at least one egress window with a window well that meets these minimum dimensions:
| Requirement | Minimum Value |
|---|---|
| Window well width | 36 inches (91 cm) minimum |
| Window well depth (projection from wall) | 36 inches (91 cm) minimum |
| Window well floor area | 9 square feet (0.84 m²) minimum |
| Clear opening of window | 5.7 sq ft (0.53 m²) minimum |
| Window opening height | 24 inches (61 cm) minimum |
| Window opening width | 20 inches (51 cm) minimum |
| Maximum sill height from floor | 44 inches (112 cm) |
Window Well Depth Rule: If the window well is deeper than 44 inches (112 cm) from the ground surface to the well floor, a permanent ladder or steps must be installed. The ladder must be at least 12 inches (30 cm) wide, with rungs no more than 18 inches (46 cm) apart, and must not encroach on the minimum 9 sq ft clear area.
Sizing Formula:
Window Well Area = Width × Projection from Wall
Must be ≥ 9 sq ft (0.84 m²)
The well must extend at least 6 inches (15 cm) below the window sill and 6 inches (15 cm) beyond each side of the window opening. Common practical sizes for standard basement windows:
| Window Width | Well Width | Well Projection | Area |
|---|---|---|---|
| 32 in (81 cm) | 44 in (112 cm) | 36 in (91 cm) | 11 sq ft |
| 36 in (91 cm) | 48 in (122 cm) | 36 in (91 cm) | 12 sq ft |
| 48 in (122 cm) | 60 in (152 cm) | 36 in (91 cm) | 15 sq ft |
Drainage Requirements: Every window well must have adequate drainage to prevent flooding. Options include:
- Gravel bed (minimum 6 inches / 15 cm deep) connected to the home’s perimeter drain system
- A dedicated sump or drain pipe connecting to the storm sewer (where permitted)
- Gravel fill of 4–6 inches (10–15 cm) at the bottom for any well
Without proper drainage, window wells collect rainwater and can flood the basement.
Window Well Materials:
- Corrugated metal: Most common, affordable, available in standard sizes. Galvanized steel resists rust.
- Masonry / concrete block: Permanent, strong, can be built to any size. More expensive to install.
- Plastic / composite: Lightweight, rust-proof, easy to install. May not last as long.
- Custom stone / brick: Decorative option for visible window wells. Most expensive.
Window Well Covers: A clear polycarbonate cover keeps out rain, snow, debris, and animals while letting light through. Covers must be easy to open from inside without tools or keys. Building codes require covers to support at least 60 PSF (adult body weight) to prevent falls.
Cost Estimates:
- Prefab metal window well (36"): $50–$150
- Installation (dig + gravel + well): $500–$1,500
- Complete egress window + well retrofit: $2,500–$5,000
- Custom masonry well: $1,500–$4,000
Important Note: Converting a basement to livable space (bedroom, home office) typically requires adding egress windows if none exist. This is a building code and safety requirement, not optional. Always check with your local building department for specific requirements and permit needs.