Home › Home & Construction › Drywall Calculator

Drywall Calculator

Planning a drywall job? Enter the total wall area in square feet and this free drywall calculator works out how many 4×8 sheets you need, how many screws to buy, and how much joint compound the job will take — with a 10% waste allowance built in so you do not run short halfway through a wall.

Common drywall jobs

How it works

Drywall is sold in sheets, and the most common sheet is 4 feet wide by 8 feet tall. That is 32 square feet per sheet. To find how many sheets a job needs, divide the total wall area by 32. A 400 square foot job needs 12.5 sheets on paper — but drywall is only sold in whole sheets, and cutting always wastes some material, so the real order is larger.

The waste allowance is the part most first-time estimators miss. Every door, window, outlet, and corner forces a cut, and the offcut left behind is usually too small or the wrong shape to use anywhere else. Sheets also get damaged: a corner gets crushed in the truck, or a cut goes wrong and the sheet has to be replaced. A 10% allowance is the standard rule for a straightforward room with a few openings. If the room has many windows, angled walls, or a ceiling with lots of light fittings, choose 15% instead — an extra sheet or two costs far less than a second trip to the store.

Screws are estimated at 32 per sheet. That works out to about one screw per square foot: screws go around the edge of each sheet and in lines down the middle, into every stud the sheet crosses. Buy screws by the box and keep the extras — they are cheap, and a box left over is useful for the next repair. Joint compound is estimated at about 1 gallon per 100 square feet of wall. That covers the tape coat, the fill coat, and the finish coat over every seam and screw head, with a little left over for touch-ups. The calculator rounds compound up to whole gallons because it is sold that way.

Measuring correctly matters more than the math. Measure every wall from floor to ceiling, multiply length by height, and add the results together. For a ceiling, measure length by width the same way. Do not subtract the area of doors and windows: the sheets that would have covered those openings get cut away anyway, and leaving them in the total acts as a small extra safety margin on top of the waste allowance. If you are drywalling a whole room, measure the walls and the ceiling separately and add them together before entering the total here.

Sheet size is worth a thought before ordering. The calculator defaults to 4×8 sheets because they are the easiest to carry, cut, and lift into place — one person can manage one, just about. Longer 4×10 and 4×12 sheets cover more area with fewer seams, which means less taping and a smoother finish, but they are heavy and awkward in a small room or up a staircase. For ceilings, longer sheets are popular because fewer seams overhead means less sanding above your head. Whichever size you choose, the formula is the same: divide the area by the sheet area, add waste, and round up.

Worked example

Sarah is drywalling the walls of a spare bedroom. She measures two walls at 12 feet long by 8 feet high (96 square feet each) and two walls at 10 feet long by 8 feet high (80 square feet each). Added together, that is 96 + 96 + 80 + 80 = 352 square feet. She rounds her entry to 400 square feet to keep the numbers simple and to cover the ceiling patch she also plans to do — and the calculator does the rest.

Step 1: Divide the area by one sheet: 400 ÷ 32 = 12.5 sheets.
Step 2: Add 10% waste: 12.5 × 1.10 = 13.75 sheets.
Step 3: Round up to a whole sheet: 14 sheets.
Step 4: Screws: 14 × 32 = 448 screws.
Step 5: Joint compound: 400 ÷ 100 = 4 gallons.

So Sarah orders 14 sheets, a box of screws (448 or more), and 4 gallons of joint compound. The 14 sheets cover 448 square feet, which is 48 square feet more than the wall area — that spare material is exactly the offcuts and mistakes the waste allowance is there for.

FAQ