How to Calculate the Size of Drywall Needed

Measure the walls for your drywall project with a tape measure. Standard walls are 8 feet high but check that. Measure the length of all walls. Multiply the height and length with a calculator to get the square footage, a 20-foot standard wall has 160 square feet. Divide that by 32, the square footage of a typical drywall panel, to get the number of sheets, 5 in this example.

Add the number of 4-foot-by-8-foot sheets needed to cover all the walls. Deduct space for large openings, like double garage doors or picture windows, but don't make allowances for standard doors and windows or other openings. Round up the total number of panels to an even figure; if the total is 21 1/2 panels, for instance, order 22.

Figure out how to use as many full panels as possible. All drywall is 4 feet wide; most sheets are 8 feet long, but sheets 10, 12 or even 16 feet can be special ordered. Use 8-foot lengths if possible, since bigger panels are hard to handle. Include in your calculations such things as cutting half-panels to start a second row, to stagger the vertical seams of the drywall. Get a couple of extra panels to allow for errors or problems; unused sheets can be returned in most cases and it's better to have extra material than to run out in the middle of a job.