Measure the length and height of the walls or length and width of the ceilings to be covered. Have a helper hold one end of the tape measure while you check the measurements. Round up all measurements to the nearest foot to ensure enough drywall for the project.
Record the measurements on a sheet of paper that shows a sketch of the wall or ceiling. Recording the measurements will help you keep the estimating in order, allowing you to make changes to individual walls or ceilings if necessary.
Multiply the length times the height when calculating the square footage of walls, and multiply the length times the width to figure the square footage of ceilings. For example, if your wall length is 10 feet long and 8 feet high, multiply 10 by 8 to get 80 square feet, and if your ceiling is 10 feet by 10 feet, multiply the two to get 100 square feet. Record the square footages under their sketches on your paper.
Add all of the square footages for the walls and record them under a total for walls. Add all square footages for the ceiling and record them under a total column for ceilings. Keep the walls and ceilings separate.
Divide the wall square footage by 32, which is the total square footage of one sheet of 8-foot drywall or the typical wall height of a drywall construction project. For example, if you have 80 square feet, divide that by 32, and you will find that you need 2.5 sheets to cover the wall. Round that number up to three sheets to account for waste. For ceilings, divide the 100 square foot sample by 48, which is the square footage of one 12-foot sheet of drywall. You would need just over two sheets to cover the ceiling. Always round up to the next measurement or sheet to ensure that you have enough material.