Drywall Calculator
Sheets, screws, mud and tape per room.
Drywall, Flooring & Interior
Wall Square Footage Calculator
Net wall area for paint, wallpaper, panelling or drywall, with doors and windows deducted.
Your result
Sample values361
Net wall area, ft²
448
Gross wall area, ft²
87
Openings deducted, ft²
56
Perimeter, ft
Walls only, two doors and three windows deducted.
What that covers
| Material | Quantity |
|---|---|
| Paint, two coats | 2.1 gallons |
| Wallpaper, standard roll | 11 rolls |
| Drywall, 4 × 8 sheets | 12 sheets |
| Panelling, 4 × 8 sheets | 12 sheets |
How to use this calculator
Enter the room dimensions and ceiling height. The perimeter is calculated from length and width for a rectangular room; for an L-shaped or irregular room, measure around the walls yourself and use the custom perimeter option.
Deduct openings at their actual sizes if you know them. The defaults are a standard interior door at 21 ft² and an average window at 15 ft², but window sizes vary enormously and three large picture windows will change the answer substantially.
Formula
Perimeter = 2 × (Length + Width)
Gross area = Perimeter × Height
Net area = Gross area − Openings
- Openings
- (Doors × Door area) + (Windows × Window area)
- Ceiling
- Length × Width, added when included
For paint, most people ignore openings under about 15 ft² and accept the small over-estimate.
Worked example
A 16 ft by 12 ft room with 8 ft ceilings, two doors and three windows, walls only.
- Perimeter: 2 × (16 + 12) = 56 ft
- 56 ft × 8 ft = 448 ft² gross
- Doors: 2 × 21 = 42 ft²
- Windows: 3 × 15 = 45 ft²
- 448 − 42 − 45 = 361 ft² net
361 square feet of net wall area
Understanding your results
Whether to deduct openings depends on what you are buying. For drywall or panelling, deduct them — you cannot reuse the offcut from a window opening. For paint, many decorators do not bother deducting anything under about fifteen square feet, because the extra paint covers the trim, the touch-ups and the second coat that always goes on heavier than the first.
Ceiling height is the input people most often estimate rather than measure. An eight foot ceiling that is actually eight foot two adds nearly twelve square feet to this room, which is most of a window. It takes a moment to check and it is the largest single source of error here.
Questions
About this calculator
Only the large ones. Deducting every small window tends to leave you short, because paint coverage figures are optimistic and the second coat always uses more than the first. Deduct openings over about fifteen square feet and treat the rest as contingency.
Walk the perimeter with a tape and add the wall lengths together, including both faces of the internal corner. Then multiply by the ceiling height. Trying to treat an L-shape as two rectangles double counts the shared wall.
Only if you switch it on. Ceilings are often painted in a different finish from walls and bought separately, so the default is walls only. When included, the ceiling is simply the room length times its width.
Roughly 350 to 400 square feet per coat on a smooth sealed surface. New drywall, bare plaster and strong colour changes all drink far more on the first coat, so treat the first coat as covering closer to 250 square feet on fresh work.
Keep going
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Estimates, not specifications.
Results are based on the values you enter and on typical material
properties. Densities, coverage rates and product sizes vary between
suppliers, so confirm quantities against your supplier's data before
ordering. Structural work must be signed off by a qualified
professional and meet your local building code.