Understanding your result
The headline is the net wall area, the board you will actually hang, and the line under it gives the number of walls, their total length and the openings taken out. The tiles add the gross area, the openings and the area in 4 × 8 sheets with no waste, a quick sense of scale.
The table lists every wall with its own arithmetic, so a sloped wall shows the trapezoid formula and a plain wall shows length times height. Below the walls are the gross total, the doors and windows subtracted at the sizes you gave, the net area and the same figure in the other unit.
To turn the area into an order, the area-to-sheets converter adds the waste and the screws, compound and tape. For a whole room with its ceiling, the room sheet calculator does the measuring for you; for the ceiling alone, use the ceiling area calculator.
How we calculate this
The door default is a rough opening of 3 ft by 6 ft 10-1/2 in, which is the opening for a 32 in pre-hung door; the window default is 3 × 5 ft. The rough opening sizes for other doors and windows are on the standard sizes table, and the rough opening calculator gives them from the unit size. Metric figures are converted exactly, at 0.09290304 m² per square foot.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Door opening | 3 ft × 6 ft 10-1/2 in (about 20.6 sq ft) | Rough opening of a 32 in pre-hung door |
| Window opening | 3 × 5 ft (15 sq ft) | A common residential size |
| Small openings | Not subtracted | Standard estimating practice: the cut-out is waste |
| Walls | Up to six, rectangles or trapezoids | Our layout |
| Conversion | 1 sq ft = 0.09290304 m² | Exact |
Assumptions last reviewed October 8, 2026.
The calculator does not handle walls with more than one slope change, curved walls (the curved wall calculator does), or arched openings. For a sheet count that accounts for how sheets fall on each wall, see the guide to counting sheets; how orientation changes the joints is in the sheet sizes and orientation guide.
Two worked examples
A stair hall: two 14 ft walls and a sloped 10 ft wall, one door
- Walls 1 and 2: 14 × 8 = 112 sq ft each
- Wall 3: 10 × (8 + 4) ÷ 2 = 60 sq ft
- Gross: 284 sq ft; one door, 21 sq ft
- Net: 263 sq ft (24.47 m²), about 8.2 sheets of 4 × 8 before waste
The sloped wall is where people over-buy: measured as 10 × 8 it would be 80 sq ft, a third too much.
Two 10 ft tall walls with three large windows
- Walls: 20 × 10 = 200 and 12 × 10 = 120 sq ft; gross 320 sq ft
- Windows: 3 × 4 × 6 = 72 sq ft
- Net: 248 sq ft, about 7.8 sheets of 4 × 8 before waste
Large windows take a big share of a wall, but the board around them is cut up; a waste allowance of 15% suits a wall like this better than 10%.
Where to find your inputs
Length. Along the floor, corner to corner, with a tape held level.
Height. Floor to ceiling at each end; for a sloped wall, at both ends.
Doors and windows. Count them and measure their rough openings, or use the defaults for standard sizes.
Walls. Up to six; run the calculator again for more, or use the room calculator for whole rooms.
Common mistakes
- Using floor area. Walls are the perimeter times the height.
- Measuring a sloped wall at its tallest point. Average the two heights.
- Subtracting outlets. They are cut out of the board; the piece is waste.
- Subtracting slab sizes. Rough openings are larger than doors and glass.
- Forgetting closets. Their walls are walls.
- Adding no waste. Area is the starting point; sheets need waste on top.
Questions people ask
- How do I calculate the square footage of a wall?
- Multiply its length by its height. A 14 ft wall that is 8 ft tall is 112 sq ft. For a wall whose top slopes, under a stair or a roof, multiply the length by the average of the two end heights; a 10 ft wall that is 8 ft at one end and 4 ft at the other is 60 sq ft.
- Should I subtract windows and doors from wall area?
- Yes, at their rough opening sizes, when you are buying drywall: about 20 sq ft for a standard interior door and 15 sq ft for a 3 × 5 ft window. Do not subtract outlets, switches and vents, because the board is cut around them and the piece removed is waste anyway.
- How do I measure a wall with a slope?
- Measure the length along the floor and the height at each end. The area is the length times the sum of the two heights, divided by two. A triangular gable is the same calculation with one height of zero.
- How many sheets of drywall for 300 square feet of wall?
- 300 ÷ 32 = 9.4 sheets of 4 × 8, and with 10% waste 10.3, so 11 sheets. With 4 × 12 sheets it is 300 ÷ 48 × 1.1 = 6.9, so 7. The area-to-sheets converter does it for any size.
- Is wall area the same as floor area?
- No. A room's wall area is its perimeter times its height, usually two to three times its floor area. A 12 × 12 ft room has 144 sq ft of floor and 384 sq ft of wall at 8 ft high.
- How do I convert square feet to square metres?
- Multiply by 0.0929 (one square foot is 0.09290304 m²). 263 sq ft is 24.4 m². The calculator shows the net area in the other unit as a row of its own.