How to calculate carpet
Start with the floor area, add waste, then convert to square yards for ordering:
Square yards = (Length ft × Width ft × (1 + waste %)) ÷ 9
A 15 ft × 12 ft room is 180 square feet. Add 10% for waste to reach 198 sq ft, which is 22 square yards.
Square feet vs. square yards
One square yard equals 9 square feet. Carpet is typically priced per square yard, so to compare with per-square-foot flooring, divide the square-yard price by 9.
What affects waste
- Room width vs. roll width: rooms wider than the roll (often 12 ft) need seams.
- Patterned carpet: matching the pattern across seams adds waste.
- Stairs and hallways: awkward shapes mean more offcuts.
Frequently asked questions
How do I calculate how much carpet I need?
Multiply the room length by the width to get the square footage, then add about 10% for waste and trimming. Carpet is often sold by the square yard, so divide the square feet by 9. A 12 ft × 15 ft room is 180 sq ft, or about 22 sq yd with waste.
Why is carpet sold by the square yard?
Carpet comes on rolls (commonly 12 feet wide), and the trade has traditionally priced it per square yard. One square yard equals 9 square feet, so to convert a per-square-yard price to per-square-foot, divide by 9.
How much extra carpet should I buy?
Add roughly 10% for standard rooms to cover trimming and pattern matching, and more for stairs, hallways, or patterned carpet where seams must line up. Rooms wider than the roll need seams, which increases waste.
Does the calculator include padding?
No — it estimates the carpet area only. Padding (underlay) is bought to the same square footage, and you may also need tack strip and seam tape. Ask your installer to confirm the full materials list for your room.
Disclaimer: This estimates carpet area only — padding, tack strip, and seam tape are extra. Have your installer confirm quantities, especially for seamed or patterned jobs.