How carpet is measured — and why square yards
Carpet is the one flooring product still quoted in two units at once. You measure your rooms in square feet, but the industry has priced broadloom by the square yard (9 sq ft) for decades, because rolled carpet comes on 12-foot-wide rolls sold by the yard of length. Many retailers now quote per square foot instead — partly because the number looks smaller — so the same carpet can be "$27 per square yard" at one store and "$3 per square foot" at another, and those are identical prices. This calculator shows both units side by side so no quote can confuse you, and adds the standard 10% waste allowance to the amount you actually order.
The formulas
Measure each room's length and width in feet; the calculator sums the areas, converts to square yards, and adds 10% for waste. In carpet-tile mode it divides your with-spare area by one tile's coverage — 2.25 sq ft for an 18 × 18 in tile, 4 sq ft for 24 × 24 in, about 2.69 sq ft for a 50 × 50 cm tile — and rounds up to whole tiles.
Worked example
A 12 × 15 ft living room (180 sq ft) plus a 10 × 12 ft bedroom (120 sq ft) totals 300 sq ft = 33.33 sq yd. With 10% waste, order about 330 sq ft (36.67 sq yd) — at $22 per sq yd that's roughly $806.67 in material.
Carpet-tile mode: the same 10 × 12 ft bedroom with 18 × 18 in tiles needs 132 ÷ 2.25 = 58.7 → 59 tiles including the 10% spare.
Seams are why the waste exists
Broadloom's 10% waste allowance isn't padding — it's a consequence of the 12-foot roll. Any room wider than 12 feet needs at least one seam, and the seamed piece must be cut so its pile direction and pattern match the main piece, which burns material. Installers also plan seams away from traffic lanes and windows (low-angle light makes seams visible), which constrains how the roll can be cut. That's also why an oddly shaped room can need noticeably more than its square footage suggests — if your layout is complex, have the installer measure before you order.
Carpet tiles sidestep the seam problem entirely: each square is its own piece, so waste drops to a spare-tiles allowance. Their quiet superpower is repair — when a tile gets stained or crushed, you lift that one square and drop in a spare, instead of living with the damage or recarpeting the room. Keep your extras from the same dye lot, since replacement tiles bought later rarely match.