The Wall Area Calculator calculates the square footage of a wall by multiplying its length by its height and subtracting doors and windows.
Use it for a single wall, for all four walls of a room (room perimeter × wall height), or for a gable end wall, where the triangular part under the roof is added: A = W × E + ½ × W × (peak − eaves). The net area is what you use for paint, drywall, wallpaper, paneling or siding estimates.
Wall Area Calculator
Square footage of a wall, all walls of a room, or a gable wall — with doors and windows subtracted.
Formula
- Single wall: A = L × H − openings
- All walls of a room: A = 2(L + W) × H − openings
- Gable wall: A = W × E + ½ × W × (P − E)
- Openings: doors × (door width × door height) + windows × (window width × window height)
Where L = length, W = width, H = wall height, E = height to the eaves, P = height to the peak.
How the Calculation Works
Step 1: Find the gross wall area (length × height, or perimeter × height for a room).
Step 2: Calculate the area of every door and window.
Step 3: Subtract the openings to get the net area. For a gable, add the triangle above the eaves.
Variables Explained
| Input | Meaning | Unit |
|---|---|---|
| Wall length / room length and width | Horizontal size | ft, m |
| Wall height | Floor to ceiling (or eaves) | ft, m |
| Height to peak | Floor to the top of a gable | ft, m |
| Doors, windows | Number and size of openings | in, ft, m |
Example Calculation
Single wall
Given: 20 ft × 8 ft, one 36 × 80 in door, one 36 × 48 in window
Result: 160 − 20 − 12 = 128 ft²
All walls of a room
Given: room 14 × 12 ft, 8 ft walls, the same door and window
Perimeter: 2 × (14 + 12) = 52 ft; gross: 52 × 8 = 416 ft²
Result: 416 − 32 = 384 ft²
Gable wall
Given: 24 ft wide, 8 ft to eaves, 14 ft to peak
Result: 24 × 8 + ½ × 24 × 6 = 192 + 72 = 264 ft²
Common Area Conversion Table
| Unit | Equivalent |
|---|---|
| 1 m² | 10.7639 ft² |
| 1 yd² | 9 ft² |
| 100 ft² | 1 “square” (siding and roofing unit) |
Material Estimation Notes
Wall area is a starting point, not a shopping list. Paint depends on coats and coverage; drywall, panels and siding come in fixed sizes and need extra for cuts. Use the Paint, Drywall, Wall Panel or Wall Siding calculators to convert area into quantities.
Waste Factor Considerations
Walls with many small openings or angled gables usually produce more offcuts. Whether to subtract small openings depends on the material — for sheet goods, pieces cut from openings are often waste anyway.
Frequently Asked Questions
How do you calculate the square footage of a wall?
Length × height, minus the area of doors and windows.
How do you calculate the wall area of a room?
Add the room length and width, double it (the perimeter), multiply by the wall height and subtract openings.
How do you find the square footage of a gable?
Rectangle below the eaves plus the triangle: ½ × width × (peak height − eave height).
How big is a standard door for wall area purposes?
Measure yours: a 36 × 80 in door is 20 ft². Enter your actual door and window sizes for accuracy.
Should I subtract windows when painting?
Yes, for a closer estimate. Painters sometimes skip very small openings.
