How Much Carpet Do I Need? Roll Widths, Seams and Square Yards

To work out how much carpet to order, you do not just multiply the room's length by its width. Carpet comes off a roll that is usually 12 ft wide (sometimes 15 ft), and you buy a length of it. So you need to know how many strips as wide as the roll will cover the floor, and how long each strip must be. A 15 × 12 ft room is 20 square yards of floor, and it takes a single 15.25 ft strip off a 12 ft roll: 20.3 square yards.

Step 1: Measure the room

Measure the length and width at the widest points, and include closets and doorways that will be carpeted. If the room is not a rectangle, divide it into rectangles and plan each one. Stairs, with their treads and risers, are best measured and ordered on their own.

Step 2: Fit strips across the room

Strips of carpet can run along the length of the room or along its width. For each direction, divide the width of the room across the strips by the roll width and round up: that is the number of strips. Multiply by the length each strip must run, plus about 3 in for trimming. The better direction is the one that uses less carpet.

This is why rooms that are just wider than the roll cost so much more. A 13 ft room needs two 12 ft strips, and one of them is mostly cut away.

Length to order for common room sizes

With 3 in of trimming per strip, using the better direction for each room, and showing how much of what you buy ends up as waste:

For a room such as 13 × 15 ft or 14 × 16 ft, check the other roll width, because the 15 ft roll can save a seam as well as carpet. Use the carpet calculator for your own room.

Seams, pattern and pile direction

• Pile direction. Carpet has a nap, which catches the light differently from different sides. All strips must run in the same direction, or a seam between them shows as a color change.
• Patterns. A patterned carpet has to line up at the seams, so each strip must start at the same point in the pattern. Add one full pattern repeat for each strip, and ask the store for the repeat length.
• Seam placement. Seams are least visible away from doorways and heavy traffic, and when they run along the direction of the light from the main window, not across it.
• Dye lots. Buy all of the carpet at once from the same dye lot. A top-up later may not match.

Pad, tack strip and the rest

Carpet pad is bought by the square yard, and is cut to the floor area: it does not need the extra length that carpet does. Tack strip goes around the perimeter, about 2 × (length + width) in feet before deducting doorways. You will also need seaming tape if there are seams, and transition strips at doorways where the carpet meets another floor.

Check before you order

• Measure twice and have the installer check it. Carpet cannot be returned once it is cut.
• Ask whether the price is per square yard or per square foot, and whether it includes the pad and installation. A price of $4 per square foot is $36 per square yard, so check which unit a quote uses.
• For a floor with different levels, closets and a bay, ask the store to lay the pieces out on a plan, which makes the best use of the roll.