How Much Carpet Do I Need?

Carpet calculation is different from other flooring because carpet comes in fixed-width rolls. You can't just order the exact square footage — you must account for the roll width and seam placement, which creates unavoidable waste.

The Roll-Width Problem

Standard residential carpet comes in 12-foot-wide rolls (commercial: 15 ft). When your room is wider than the roll, you need multiple strips seamed together. For example, a 15 × 14 ft room with a 12 ft roll needs 2 strips, each 15 ft long:

  • Strip 1: 15 ft long × 12 ft wide = 180 sq ft
  • Strip 2: 15 ft long × 12 ft wide = 180 sq ft
  • Total carpet ordered: 360 sq ft (40 sq yd)
  • Room area: 210 sq ft (23.3 sq yd)
  • Excess (unavoidable waste): 150 sq ft (16.7 sq yd)

How to Calculate Carpet Quantity

  1. Determine strips needed: ceil(room width ÷ roll width)
  2. Calculate carpet length: strips × room length
  3. Calculate carpet area: carpet length × roll width
  4. Convert to square yards: carpet area ÷ 9 (carpet is priced per sq yd)
  5. Add waste allowance: × 1.10 (for cuts, pattern matching, seaming)

When the Room Fits the Roll Exactly

If your room width equals the roll width (e.g., a 12 × 15 ft room with a 12 ft roll), you need exactly 1 strip with no excess. The carpet area equals the room area, and waste is minimal. This is the ideal scenario.

Pattern Matching

Patterned carpet (stripes, geometric designs) requires additional waste for pattern alignment across seams. Increase the waste factor from 10% to 15% for patterned carpet.

Use the Carpet Calculator

The Carpet Calculator handles the roll-width calculation automatically. For general hard flooring (laminate, vinyl, hardwood), use the Flooring Calculator instead — it doesn't need to account for roll width.

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