A yard is three feet. A square yard is three feet by three feet, or nine square feet.
If your carpet is priced per square yard, divide your area by nine to get the price per square foot. 11' x 13' is 143 square feet, or 15.9 square yards.
But there's a problem. Since carpet usually comes in twelve foot rolls, you'll have some scrap. They will cut off one side to meet your 11 foot width, and most likely they'll need a piece at least 12 x 13 feet. So you'll pay for at least 156 square feet (17.3 square yards) of carpeting, plus padding and installation if that's not included.
If your carpet is priced per square yard, divide your area by nine to get the price per square foot. 11' x 13' is 143 square feet, or 15.9 square yards.
But there's a problem. Since carpet usually comes in twelve foot rolls, you'll have some scrap. They will cut off one side to meet your 11 foot width, and most likely they'll need a piece at least 12 x 13 feet. So you'll pay for at least 156 square feet (17.3 square yards) of carpeting, plus padding and installation if that's not included.