Drywall calculator: what do I need to buy?

How the drywall calculator works

Start with the tape. Type each length the way it reads: 14' 6", 14 ft 6 in, or a plain 14.5. A number on its own means feet for rooms and walls and inches for doors and windows, and the calculator reads every entry back beside its label before it multiplies anything. That's where a window typed as 36 feet gets caught, before it costs you a sheet.

The walls are the distance around the room times its height: 2 × (length + width) × height. Each door and window comes off at the size you measured. We don't plug in a "standard" door. Closet doors, patio sliders and basement windows all run their own sizes. The ceiling is length times width, and it stays out until you switch it on. Walls and ceiling are separate groups, each with its own sheet size and its own framing, because the 4 × 12 that makes sense overhead isn't always the sheet you want on a 9-foot wall.

For sheets, the calculator takes the wall area, adds any waste you asked for, divides by the area of one sheet and rounds up once. It's an area count, so it assumes the offcuts get used somewhere else in the room. Right under it sits a second number, the count with the openings left in, because a window's hole usually comes out of a sheet you paid for anyway. In a 14 by 12 room with a door, two windows and 10% waste, that's 13 sheets of 4 × 8 with the openings out and 15 with them in. If your hanger cuts openings out of full sheets, plan on the second number.

Screws come from the building code's spacing instead of a guess at the box. IRC Table R702.3.5, the same in the 2021 and 2024 editions, puts screws no more than 12 inches apart on ceilings. On walls it's 16 inches over studs 16 inches apart, but 12 inches over studs 24 inches apart. The calculator counts how many framing lines a sheet crosses and how many screws fit along each, then spreads that over the board you hang. It's a minimum, which is why the line says "at least," and nothing stops your hanger driving more. Hang a 4 × 8 vertically over 24-inch studs and it takes 27 instead of 25.

The calculator counts mud and tape on the board you hang rather than the sheets you buy, since both manufacturers print their figures per 1,000 square feet of board on the wall. Put the example room's 10% waste into the mud and you'd buy 5.94 gallons instead of 5.4 for drywall that never goes up. USG prints about 10 gallons of all-purpose compound and about 370 feet of paper tape per 1,000 square feet; ProForm prints 9 gallons and 350 feet. We use the higher figure for each. Running short halfway through a coat is the worse mistake. The label on your own bucket beats both of them: type its figure and it replaces ours.

Two jobs stay outside the arithmetic. IRC Table R702.3.5 gives Type X board on a garage ceiling under living space its own row, with fasteners 6 inches apart, and the calculator doesn't count it. Tub and shower walls are the other. The code is blunt about water-resistant drywall: it "shall not be used where there will be direct exposure to water". Those walls take cement or glass-mat backer board, which the tile calculator and your installer handle.

Who this is for

Homeowners finishing a basement, re-drywalling a bedroom after a leak, or turning a garage into an office, with the tape-measure numbers in one hand and the store's app in the other.

Anyone holding a contractor's materials list or a delivery ticket that says "16 sheets, 2 buckets" and wanting to know whether the room really needs all of it.

Anyone patching one wall who'd rather not buy a third sheet just to be safe.

How much drywall do I need?

Measure each room along the floor and up one wall, then add the ceiling if it's getting new board. Take off the doors and windows you won't cover, divide by one sheet's area, and round up once. That's the sheet count. Mud, tape and screws follow from the board you actually hang: about 10 gallons of all-purpose compound and 370 feet of paper tape per 1,000 square feet on USG's figures, and screws at the spacing the code sets for your studs and joists.

Every figure the calculator uses sits under its line, with its source, so you can argue with any of them. In Britain they'd call this a plasterboard calculator. Same arithmetic, different accent.

Sources and last checked

Code figures read October 4, 2026; manufacturers' sheets checked October 7, 2026. Data version drywall-quantity-figures 2026-10-07.

• Screw spacing and screw length: International Residential Code 2021 and 2024, Table R702.3.5 and section R702.3.5.1 (International Code Council). The IRC is a model code; states and towns adopt it with amendments.
• Joint compound: USG Sheetrock Brand All Purpose Joint Compound submittal (J1969, rev. 6-22); USG UltraLightweight joint compound submittal (J2051, rev. 6-22); ProForm All Purpose Joint Compound submittal (rev. 10 25) and product page.
• Paper tape: USG Sheetrock Brand Paper Joint Tape submittal (J443727, 7-26; the earlier J1736, rev. 10-15, prints the same figure); ProForm's materials estimating table.
• Sheet sizes, panel weight, screw length for a 1/2 inch panel: USG Sheetrock Brand UltraLight Panels submittal (WB2501, rev. 4-20).

One gap in the screw count, as of October 8, 2026. Section R702.3.5 wants each sheet end that runs along the framing to land on a stud or joist. When a sheet's length isn't a whole number of framing spaces, like a 4 × 10 over 16-inch studs, that end falls between two, and the count leaves out the screws for the stud or blocking you add there.

Your list is plain arithmetic on the numbers you type. We name the makers for what their own sheets print and don't recommend one over another. Sheetrock is USG's trademark and appears here only in the names of USG's documents.