How to Calculate Square Yards for Carpet
Being able to calculate the square yards for new carpet in a room seems relatively simple at first. However, several considerations can affect the actual number of square yards of carpet that you will need to purchase for a room. The type of carpet you choose may affect how much you need to purchase.
While multiplying the length times the width of a room yields the actual square footage, the width the carpet is manufactured in and seam locations must be considered as well. How do you calculate square yardage for carpet?

Measure the length and width of the room to calculate the square yardage of carpet needed. Start the measurement in the center of doorways to allow the carpet to meet the floor covering in the next room, or simply add about 2 inches to each measurement. Be sure to measure the longest and widest areas of the room.

Draw a diagram of the room. Calculations will be easier if you are able to draw your diagram to scale. For example, use a scale such as one centimeter equals one foot. Be sure to include all doorways, closets, fireplaces and other builtin features of the room in your diagram.

Plan the layout of the carpet on your diagram. If the width of the room is less than the width of your chosen carpet then multiply the width of your chosen carpet, either 4 or 5 yards, times the length of the room. For example, say the room is 9 feet wide (3 yards) and 18 feet (6 yards) long. The actual square yardage needed is 3 yards x 6 yards, or 18 square yards. However, that would result in a seam down the center of your room. To avoid a seam, use the width of the carpet, 4 yards for our example, times the length of the room, 6 yards, and purchase 24 square yards of carpet.

Add 10 percent to the total square yardage needed when installing Berber or patterned carpets to allow for pattern matching during installation when a seam will be necessary.
Things You Will Need
 Measuring tape
 Calculator
 Diagram
Tip
Add 2 extra inches to length and width if measuring from the base of the walls. Having a seam may allow you to purchase less carpet, saving money. Seams are less obvious with shag type carpets.
Warning
Avoid having two pieces of carpet meet perpendicular to a doorway; the seam will wear and show much sooner. Seams typically wear faster than the rest of the carpet, so you might end up replacing the carpet sooner.