- 1). Measure the length and width of a floor surface using your tape measure. Multiply these numbers to find the square footage of that room. Measure odd areas of the room separately (such as a closet) and then add to the total.
- 2). Repeat Step1 in any remaining rooms, then add the square footage calculations together to find the total square footage to be covered with flooring underlayment.
- 3). Divide the total square footage of the floor by the area of the material being used for underlayment (most underlayment types are available in 4-by-8-foot sheets with an area of 32 square feet). Add 10 percent to this amount to account for wasted material. Multiply the amount of material by its unit price.
- 4). Multiply the total square footage of the floor by 12 (this will calculate the total floor area in inches), then divide this number by 16 (most underlayment types will be nailed off at 16 inches on center) to find the total number of nails needed per your floor area. Add 10 percent to this number to account for wasted material, then multiply by their unit price.
- 5). Add the costs you calculated from Steps 3 and 4 to find the total cost of materials for this project.
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