How do you calculate the amount of drywall needed for a project?

To calculate the amount of drywall needed for a project, measure the height and width of the walls or ceilings to be covered. Multiply the height by the width to get the square footage. Subtract the area of any doors or Windows. Divide the total square footage by the size of the drywall sheets (usually 4'x8') to determine how many sheets are needed.