Square feet vs. square yards
Rooms are measured in feet, but carpet is priced and sold in square yards. The conversion is simple once you have the area:
Area (sq ft) = Length ft × Width ft
Square yards = Area (sq ft) ÷ 9
The ÷ 9 comes from the fact that one square yard is a 3 ft × 3 ft square, which covers 9 square feet. So a 180 sq ft room needs 20 square yards of carpet before any waste allowance is added — and after the standard 10% allowance, that same room comes to 198 sq ft, or 22 square yards.
Carpet has been sold this way since rolls were manufactured in widths closer to a yard, and the convention never went away. Most carpet retailers still quote a price per square yard, so converting your room's square footage is the first real step in budgeting a job, not just a formality.
Why you need a waste allowance
Carpet rolls come in standard widths — most often 12 ft, with 13 ft 6 in and 15 ft also available from some manufacturers. Unless your room happens to match the roll width exactly, the installer has to cut and piece the carpet to fit, and every cut produces some amount of unusable offcut.
- Seams: rooms wider than the roll need two or more strips seamed together, and the strips have to overlap slightly before the seam is cut and joined.
- Pattern matching: patterned or textured carpet has to line up across a seam, which means shifting one strip further down the roll to align the pattern — and the material skipped over in that shift is wasted.
- Pile direction: carpet pile has a nap, or direction it leans, and every strip in a room needs to run the same way for the color and texture to look consistent. That constraint limits how efficiently strips can be laid out side by side.
5% is enough for a simple rectangular room with plain, non-patterned carpet. 10%, the default here, covers a typical room with a seam or two. Reach for 15% or higher when the carpet has a repeating pattern, the room has an irregular shape, or there are a lot of closets, hallways, and doorways feeding into the space.
Measuring irregular rooms
This calculator works on a single rectangle, so an L-shaped room, a room with a bay window, or one with a closet alcove needs to be broken into smaller rectangles first.
Sketch the room from above, then draw one or more straight lines to divide it into rectangular sections — an L-shaped room, for instance, splits cleanly into two rectangles. Measure the length and width of each section, calculate the square footage of each separately, and add the results together before running the total through this calculator's waste allowance and square-yard conversion.
Closets are usually carpeted along with the room they open into, so include their floor area in your measurement unless you plan to leave them bare. Doorways don't need to be subtracted — carpet runs underneath a door casing the same as it does anywhere else in the room.