Carpet Calculator

Carpet is one of the last flooring materials still sold mainly in square yards, a holdover from pre-metric industry tradition. How the material is rolled and cut drives the estimate, so it is worth understanding before you order.

Why Square Yards Matter

The carpet industry settled on square yards long before anyone in the US was thinking about metric. One square yard is 9 square feet.
A 12 by 15 foot bedroom is 180 sq ft, which is 20 sq yards. Installers, retailers and price lists all quote per square yard, so your tape-measure numbers have to be converted before anyone can quote you.

The 12-Foot Roll Width Rule

Carpet is manufactured in rolls 12 feet wide, with a few products at 13 ft 2 in or 15 ft. That single number decides where your seams go. A room whose narrower dimension is under 12 feet can be covered by one lengthwise strip with no seam at all, however long the room is. A 20 by 10 room is fine. A 14 by 13 room is not, and needs a seam where two strips meet.

Seam placement is an art. Installers put seams perpendicular to the main light source, usually the window, because light raking along a seam parallel to the glass lights it up like a scar. Keep them out of traffic paths where you can.

Waste Factors

Solid-color or textured carpet with no pattern: 10% covers cuts, seams and the fact that no room is truly square.

Patterned carpet is a different animal. Waste tracks the pattern repeat, because every strip has to start at the same point in the pattern to line up. A 24-inch repeat on a 15-foot room can cost you up to 2 feet on each strip. Estimators add 15 to 20 percent for patterned goods, and on a busy geometric they add more.

Carpet Pad

Do not skip the pad. It carries the comfort, the sound deadening and most of the carpet’s service life, and a cheap pad under good carpet wears the carpet out early. Standard residential pad is 6 lb rebond foam at 1/2 inch. Premium is 8 lb at 1/2 to 5/8 inch. It is sold by the square yard and should match your carpet yardage. Budget roughly $2 to $4 per sq yd, approximate and moving with the year.

Tack Strips and Seam Tape

Tack strips run the perimeter of every room and hold the stretched carpet down. Budget about 1 linear foot of strip per linear foot of wall, minus the doorways. Installed cost runs roughly $0.50 to $1.00 per linear foot, again approximate.

Stair Calculation

Stairs eat far more carpet than people expect, and the widely repeated “about a square foot a step” is nowhere near it. Work it out per step instead:

• Tread depth: about 10 inches
• Riser height: about 7.5 inches
• Wrap under the nosing: about 1.5 inches
• Run of carpet per step: about 19 inches, which is 1.58 ft

On a 36-inch-wide staircase that is 1.58 × 3 = 4.75 sq ft per step. A standard 13-step flight therefore takes about 62 sq ft, roughly 7 square yards, before any waste. Add a landing and you are past 8. The calculator uses the same 19-inch figure and lets you set the stair width.

A waterfall installation, where the carpet drops straight from the nosing to the next riser, uses slightly less. Cap-and-band, where it wraps the nosing and returns underneath, uses slightly more. The 19 inches above sits between them.

Real Estimating Example

Two bedrooms:

• Room 1: 12×15 = 180 sq ft = 20 sq yd
• Room 2: 11×13 = 143 sq ft = 15.9 sq yd
• Total: 323 sq ft = 35.9 sq yd
• With 10% waste: 35.9 × 1.10 = 39.5, so order 40 sq yd
• At $8/sq yd carpet, $3/sq yd pad and $4/sq yd install, that is $15/sq yd × 40 = $600

Cost Ranges

These are approximate US figures that move with grade, region and year. Price the job against your own quotes rather than these numbers, and if you are working in another currency the calculator will follow whatever you pick in the site header:

• Builder-grade carpet plus installation: $5 to $9 per sq yd
• Mid-range carpet plus installation: $9 to $15 per sq yd
• Premium carpet plus installation: $15 to $30 and up per sq yd

Get two or three quotes from local installers. The spread between them on the same job is routinely 30 percent, and the cheapest one is not always the one cutting corners.