Carpet Calculator

How much carpet do I need?

Start with the room area — length times width — but do not stop there, because carpet is not sold by the area you need. It comes off a roll in a fixed width, almost always 12 ft in the United States, sometimes 13.5 ft or 15 ft, and 4 m in much of Europe. The installer unrolls it, cuts strips that run the length of the room, and joins them. Whatever falls outside those strips is off-cut you still pay for. That is why two rooms with identical square footage can need very different amounts of carpet.

This calculator lays your room out in strips both ways round — running the length and running the width — keeps the cheaper cut, then adds the waste allowance for trimming, door recesses and pattern matching. The result is the number to give a retailer, not the bare floor area.

Worked example: a 15 ft x 12 ft living room

The floor area is 15 x 12 = 180 sq ft, which is 180 ÷ 9 = 20 sq yd. On a 12 ft roll, one strip 12 ft wide and 15 ft long covers the whole room: no seam, no strip waste. Add the standard 10% allowance and you order 198 sq ft, or 22 sq yd. This is the happy case, and it is exactly why 12 ft rolls exist — American rooms were designed around them.

Now widen the room to 14 ft. The area is 15 x 14 = 210 sq ft, but a 12 ft roll cannot cover 14 ft in one pass. You need two strips: 2 x 12 ft x 15 ft = 360 sq ft of carpet for a 210 sq ft room, before waste. Turn the layout 90 degrees and it is two strips of 12 ft x 14 ft = 336 sq ft — slightly better, which is the cut this tool would pick. Either way you are buying roughly 60% more carpet than floor. A 15 ft roll covers the same room in one pass: run it across the 15 ft direction and a single 14 ft length of roll does the whole floor — 15 x 14 = 210 sq ft, seam free, zero strip waste, and about a third less carpet than the 12 ft roll. Always ask what roll widths the pattern you like is made in.

The square yard quote trap

Carpet retailers quote in both square feet and square yards, and the two differ by a factor of nine. A showroom price of $27 per square yard is $3.00 per square foot. An online listing at $4.50 per square foot is $40.50 per square yard. Shops know that the per-square-foot number looks smaller and often lead with it, then quote the installation per square yard. Before you compare anything, put both quotes in the same unit — this calculator gives you the quantity in both, and the price selector multiplies by whichever basis you were quoted.

The other half of a real quote is what is included. Ask specifically whether the number covers padding, tack strip, subfloor prep, furniture moving, removal and disposal of the old carpet, stair charges (usually priced per stair, not per yard) and metal transition strips at doorways. A $2,000 carpet job with $900 of extras is not cheaper than a $2,600 all-in job.

Choosing padding — the part people skip

Padding is measured by density in pounds per cubic foot, not by how soft it feels in the shop. Density is what resists compression, and compression is what destroys carpet backing. The industry rule of thumb for residential cut pile is 8 lb density at 7/16 in thickness; most carpet warranties set a floor of 6 lb and a ceiling of 7/16 in, and a pad thicker than that lets the carpet flex enough to break the backing at seams and traffic lanes. Berber and other low-profile loop carpets want firmer, thinner pad — 8 lb at 3/8 in — because a soft pad under a stiff loop backing cracks it.

Padding is bought to the room area, not the strip area, which is why the padding figure here is lower than the carpet figure. It is also the cheapest upgrade in the whole job: moving from a builder-grade 6 lb pad to an 8 lb rebond typically adds well under a dollar per square foot and adds years to the carpet's life. Basements are the exception where you should spend on the pad rather than the carpet: use a moisture-barrier or synthetic fibre pad rather than rebond foam.

Installation day checklist

Measure the room at its widest points, including any doorway recesses and the depth of closets, because carpet runs through both. Empty the room, or agree in writing what the crew will move and what they will not — pianos, aquariums and anything electronic are usually excluded. Confirm the seam plan before the knife comes out: you want seams out of doorways, out of the main walking path and perpendicular to the main window rather than running toward it. Check the pile direction is consistent across every strip; carpet has a nap, and a strip laid backwards shows as a different shade forever. Keep an off-cut of at least a square yard for future patch repairs, and let the room air for a day or two, as new carpet does off-gas.

Limits of this estimate

The tool models one plain rectangular room. L-shaped rooms should be split into rectangles and run separately, then add a strip's worth of allowance for the joining piece. Stairs are priced and measured differently — budget roughly 1.5 sq yd per straight step including the riser, and considerably more for winders or a landing. Hallways longer than a roll are almost always the worst case for waste, and a 15 ft roll or a seam plan that runs down the length rather than across it can halve that cost. Finally, the waste allowance is exactly that: an allowance. If you are working with a large pattern repeat, an irregular room, or a fitter who has not seen the space yet, take a professional measure before you order, because carpet is cut to order and you cannot return an off-cut.