Determining drywall square footage helps the builder determine the amount of materials necessary for the project. Use the measurement to estimate labor requirements. The calculations are basic mathematics for rectangular or square rooms. Convert the square footage into the number of sheets of drywall when purchasing material.

Measure the length of each wall in the room. State the measurements in feet and fractions of a foot. For example, a wall that is 10 feet 6 inches long would be listed as 10.5 feet long.

Measure the height of the walls. This is commonly just under 8 feet. You may wish to round this distance to 8 feet as the inch or two trimmed from the drywall will all be waste material.

Multiply the length of the wall times the height of the wall. This produces the square footage of that wall. For example, if the wall is 10 feet long and 8 feet high it totals 80 sq. ft.

Add together the total square footage of each wall for the total wall square footage of the room.

Calculate the square footage of each door and window in the room. Measure the height and width of each and multiply to determine the square footage of each opening. Add together the total square footage of each opening.

Use the length and width of the room from previous steps to calculate the square footage of the ceiling. Multiply the width by the length to determine square footage of the ceiling.

Subtract the square footage of the openings from the total square footage of the wall before adding the square footage of the ceiling to determine the total square footage of drywall in the room. Repeat the process for all rooms in the project.