Drywall Calculator
Calculate how many drywall boards you need for walls, and optionally the ceiling.
How we calculate it
Boards = ceil(Total area / Board area × (1 + Waste factor)), where total area is wall area (perimeter × height) plus the ceiling area, if included.
Understanding your estimate
Buying drywall by eyeballing a room is how you end up back at the store mid job, or driving home with two sheets you'll never use. This calculator works off perimeter and wall height, the same two measurements you'd already use for paint, and adds the ceiling only when you actually check that box.
A bedroom with a ceiling, worked out
Say you're covering a room with a 40 ft perimeter and 8 ft walls, including the ceiling of a 10 ft by 10 ft room, using standard 4×8 ft sheets and the default 10% waste factor.
- Wall area: 40 × 8 = 320 ft².
- Ceiling area (10 ft × 10 ft room): 100 ft².
- Total area: 320 + 100 = 420 ft².
- Divide by the board's coverage, 32 ft² for a 4×8 sheet: 420 ÷ 32 = 13.125 sheets.
- Apply the 10% waste factor: 13.125 × 1.10 = 14.4375.
- Round up: 15 sheets. That's what you buy, not 14 and a fraction.
Why walls are perimeter times height, and the ceiling is optional
Perimeter and wall height are the same pair this site's Paint Calculator already uses, and that's deliberate: if you've measured a room for paint, you've already measured it for drywall. The alternative would be asking for a single total area, quick to type but easy to get wrong, or asking for a list of every wall and opening one by one, accurate but more form than most jobs need. The ceiling sits in between, as its own optional step. Leave the checkbox off and the calculator never asks for a room length or width at all, because the function underneath treats the ceiling as an argument you either pass or don't, not a field it has to guess whether you meant to fill in.
Why board size is a menu, not a text field
Our Tile Calculator lets you type any tile dimension you want, because tile comes in whatever size the manufacturer cut it. Drywall doesn't work that way: a sheet is 4×8 ft, 4×12 ft, or the metric 1.2×2.4 m panel, full stop, so this calculator offers those three as a dropdown instead of two blank fields for length and width. The metric option isn't a separate number tuned for a different market either. It's the same physical sheet as the 4×8, measured in square meters and converted to square feet behind the scenes, the way you'd convert any area. That's different from how this site handles paint coverage, where a gallon's coverage rate genuinely is a different number depending on which unit system you're buying in, not a straight conversion of the same physical fact.
Why the waste factor defaults to 10%, and the sheet count never rounds down
There's no official waste percentage for drywall, the way there's a slope table for stairs. Ten percent is the same default this site uses for tile laid in a straight pattern, and the logic transfers cleanly: cutting a rectangular sheet to fit around a corner or a doorway wastes material in roughly the same proportion, whether that sheet is ceramic or gypsum. Change the field before calculating if your job has more cuts than a simple rectangular room, a lot of jogs and closets, say, but 10% is a reasonable place to start.
The 14.4375 sheets from the worked example above never becomes 14. This calculator rounds every sheet count up, not because gypsum board is expensive enough to obsess over a fraction, but because coming up one sheet short means a second trip to the store with a half hung room waiting on you. A leftover sheet costs you the price of a sheet. A missing one costs you the rest of your afternoon.
What this calculator does not subtract
This calculator does not subtract doors or windows from the total area, and that's not an oversight. Our Paint Calculator does subtract openings, because the paint you would have used on a window pane is paint you simply don't buy. Drywall doesn't work that way. A sheet cut to fit around a door still came out of a full sheet, and that offcut rarely lines up with what the next wall needs, so treating an opening as free square footage would leave you short at checkout. If your room has an unusually large opening, a garage door wall or a bank of windows, measure that wall's remaining drywall by hand rather than trust a subtraction this calculator was never built to make.