Calculate square footage. Measure the length of the room and the width of the room in feet and multiply those two numbers.
Convert the square footage to square yardage if you want to price carpet before you buy. Keep in mind that 1 square yard equals 9 square feet. Divide the total number of square feet by nine to get your square yardage.
Consult a professional carpet salesperson or installer before making your purchase. A professional will be able to assist you with elements of carpet purchasing that you probably aren't aware of. If you are purchasing patterned carpet, for example, you'll have to match up the pattern at the seams, which may require additional carpet.