How to Measure a Surface Finish

Measure the area of the wall surface to be covered. Use a tape measure to find the height and length of the wall. For a rectangular or square wall, multiply length times width to obtain the area of the space. For trapezoidal walls, calculate the area of the rectangle portion. Calculate the area of the right triangle portion by measuring the base and the height. Multiple base times height, then multiply this by one half.

Check the label of the paint for the total surface area the gallon or quart covers. A gallon of paint covers from 150 to 400 square feet, depending on the wall type and how the paint is applied. Now double the area of the surface. Most walls take two coats of paint for complete coverage. Compare this calculation to the smallest number of square feet the container of paint covers to safely determine how many gallons of paint to buy.

Use the formulas for measuring area to determine wallpaper finish coverage. Deduct 15 square feet per any average-sized door or window openings in the room. Wallpaper comes in rolls usually 21 to 36 inches wide. Single rolls of wallpaper contain 36 square feet. If working with a pattern, determine how many inches between pattern repeats, and always round up to the nearest inch. Then divide the wall height in inches by the length of the repeat. Take that number and multiply it by the original number of inches between pattern repeats. That final calculation is the new wall height you should use when finding the area of the wall. For example, if the pattern repeats every 10 inches and the wall is 8 feet tall, your formula will look like this: 96/10 = 9.6; 10 x 10 = 100; 100/12 = 8.3 feet. The new height to calculate square footage on the wall is 8.3 feet.

Measure the area of the floor to be covered with a finish. Calculate the area the same way as with a wall. Wood varnishes also indicate the number of square feet covered per container. Use the method to determine how much paint to use on a wall to find out how much varnish you will need.

Find the area of the floor to be carpeted. If carpeting multiple rooms, measure and diagram each room separately. Because carpets commonly come in 12 feet rolls, consider widths of 12 feet when measuring the room. If the room is 11 feet wide and 15 feet long, the actual amount of carpet will be 12 times 15. Usually carpet is sold by square yards, not feet, so measure the area then divide by three to get an approximate square yardage. Because of complications from matching carpet patterns and determining where the seams should be, always have the carpet installer make a final measurement before ordering carpet.