Carpet calculator: square feet and square yards

Carpet has been sold by the square yard for decades, even though most American flooring uses square feet. One square yard equals 9 square feet, so a 200 sq ft room is about 22.2 sq yd.

When comparing prices, always convert. Carpet at $4/sq yd is much cheaper than carpet at $4/sq ft — about 4.5 times cheaper, in fact.

Carpet typically comes in 12 ft and 15 ft widths. If your room is 13 ft wide, you’ll need a 15 ft roll and waste 2 ft of width across the room — or use seams.

A skilled installer can hide seams in low-traffic areas, but seams will always be slightly visible on cut-pile carpets. Plan your room dimensions and roll choice carefully.

US carpet comes almost exclusively in 12-foot rolls, with 15-foot wide and 13.5-foot wide rolls available from premium manufacturers. Roll width is the single most important factor in determining whether your installation will have seams — and where.

If your room's shorter dimension is 12 feet or less, you can usually do a seamless install with a standard 12-foot roll. If it's between 12 and 15 feet, you'll either need a wide-roll carpet or accept a seam. Over 15 feet on the short side, seams are unavoidable.

Worked example: a 14 × 18 ft master bedroom (252 sq ft = 28 sq yd). Option A — 15-ft roll: 15 × 18 = 270 sq ft, no seam, 18 sq ft waste, order 30 sq yd. Option B — 12-ft roll: 12 × 18 main piece + 2 × 18 seam strip = 252 sq ft exactly, plus 10% waste = 31 sq yd, with one seam parallel to the long wall. Option A is cleaner but limits color selection.

Stair carpet calculation is fundamentally different from room carpet because each step has both a tread and a riser plus a small return at the nosing. The pile direction also has to run consistently down all stairs, which forces wasteful cuts.

Standard formula per step: width × (tread depth + riser height + 1.5 in for nosing wrap). For an average 30-inch wide stair with 11-inch tread and 7-inch riser: 30 × 19.5 = 585 sq in per step = 4.06 sq ft. A 13-step staircase: 13 × 4.06 = 52.8 sq ft = 5.87 sq yd.

Always add 20% waste for stairs (not the standard 10%) because of pile direction and the small cuts required at landings and turns. The 13-step example becomes 7 sq yd of carpet ordered.

Carpet is the one flooring material where the room's shape costs you more than its size. It comes off a roll in a fixed width — almost always 12 ft, sometimes 15 ft — and you buy the full width for every linear foot you take. Anything narrower than the roll is trimmed off and thrown away.

That makes orientation a real decision rather than a detail. Lay a 9 × 12 ft room so the 12 ft dimension runs across the roll and it uses 9 linear feet: 108 sq ft purchased for 108 sq ft of floor, with nothing wasted. Turn it the other way and you buy 12 linear feet — 144 sq ft — and bin a third of it.

The table shows the best orientation for each room, with the dimension that runs across the roll width chosen to be as close to 12 ft as possible without exceeding it. Rooms where both dimensions exceed 12 ft need a seam, and a seam is a layout decision: it should run along the line of sight from the doorway, not across it.

Worked example — an 11 × 18 ft room. The 11 ft side runs across the roll, so you pull 18 linear feet of 12 ft carpet. That is 216 sq ft purchased against 198 sq ft of floor, which is 8.3% waste before you have cut anything. Add the doorway allowance and the pattern match and it climbs further.

This is also why carpet is quoted per square yard in much of the trade. A 12 ft roll is exactly 4 yards wide, so linear yards of roll convert cleanly. Divide square feet by 9 to get square yards when comparing a quote against your own measurement.

Carpet pad is sold separately, in the same square yardage as your carpet. Pad density and thickness are spec'd in two numbers: weight (lbs per cubic foot) and thickness (inches). Higher density extends carpet life dramatically, often by 50% or more.

Common pad types: 6-pound rebond ($0.40-0.60/sq ft) is the cheap standard; 8-pound rebond ($0.60-0.80/sq ft) is recommended for most homes; memory foam pad ($1.20-2.00/sq ft) feels luxurious but compresses faster. Berber and looped carpets need a dense, thin pad (1/4-3/8 inch); plush carpets can use thicker pads up to 7/16 inch.

Most manufacturer warranties require minimum pad specs — buying cheap pad can void a $3,000 carpet warranty.