Add 10 percent when calculating how much carpet you need.
A miscalculation can cost more money to fix, or require some fast thinking and expert figuring to seam the carpet properly and hide the mistake. Making it the responsibility of the carpet seller to measure and calculate the amount of carpet required keeps him responsible for mistakes. However, it's important to know how he figured the square footage of the purchase so that you can keep costs in line.
Measure the length and width of the room requiring carpet.
Calculate the area of the floor by multiplying length by width. For example, a room that is 17 feet wide by 13 feet long is 221 square feet.
Add an extra 10 percent to the square footage to cover any extra carpet needed for seaming or for rooms that are not completely square. In this example, 10 percent of 221 square feet is 22.1. You would order 243 square feet of carpet.