Carpet Calculator

How the carpet calculator works

A 14 × 12-ft bedroom needs 21 square yards of carpet plus 21 square yards of pad. The room is 168 sq ft, or 18.7 sq yd raw; a 10% waste factor brings it to 185 sq ft (20.5 sq yd), which rounds up to 21. Off a 12-ft roll that room takes one seam, because the 14-ft dimension is longer than the roll is wide.

Carpet rolls come in standard widths — almost always 12 ft (3.66 m) or 15 ft (4.57 m). If your room is wider than the roll, you need a seam. If your room is longer than the roll, you order multiple pieces. We size the order based on these constraints, not just total square footage.

Why "square yards" not square feet

Carpet has been sold by the square yard in the US for over a century. 1 sq yd = 9 sq ft. Most US installers and stores still quote in sq yd. International / metric markets use m² directly. If you know sq ft, divide by 9 for sq yd; if you know m², it's already in the right unit.

Pile direction (the gotcha)

Carpet has a nap — fibers lean in one direction. If you rotate a piece 90° to fit it next to another piece, the nap goes the wrong way and the carpet looks two-toned even with no actual seam. Always lay carpet with all pieces' nap pointing the same direction. This is why a 13×14 ft room needs more carpet than 13×14=182 sq ft suggests — you can't rotate sections.

Roll width is nominal — plan for slightly less

A "12-foot" roll is a nominal figure. Mills run goods somewhere around 11 ft 10 in to 12 ft 2 in, and the outer few inches carry edge distortion that has to be trimmed off. So you cannot count on a full 12 feet of usable width, and a room that measures a true 12 ft wall-to-wall will not be covered by a single drop off a 12-ft roll — you need a little extra at each wall to trim and tuck into the tackless strip. This is why the seam guidance above flags a room that matches the roll width exactly rather than calling it a clean fit. When your short dimension is within about four inches of the roll width, measure again at three points; walls are rarely parallel.

Seams and waste

• Single piece (no seam) — 10% waste plenty.
• One seam — 12–15% waste. Plan the seam in a low-traffic area, perpendicular to natural light if possible (less visible).
• Multiple seams or stairs included — 18–25% waste.
• Patterned carpet — add 5–10% on top of all the above for pattern matching.

Understand what the calculator's waste factor is and is not. It is an area allowance: it scales the room's square footage up to cover trim, tuck, and offcuts. It does not simulate cutting the room out of a roll of fixed width, which is what actually determines your bill on an awkward room. For most rooms narrower than the roll the two agree closely. For a room wider than the roll they can diverge sharply, and the roll-cut number is always the larger one. The worked examples below show both, so you can see the gap before your installer does.

Fibre: the choice that decides how it looks in five years

Nearly every complaint about carpet — matting in the traffic lane, a hallway that reads darker than the bedroom, a stain that will not come out — traces back to the fibre and the construction rather than to the price. Two properties matter: resilience, the fibre's ability to spring back after being crushed, and stain resistance, which can either be a topical treatment that wears off or a property of the fibre itself.

The practical shortlist: nylon or triexta for anywhere people walk regularly, polyester for bedrooms if you want colour and softness at a price, olefin only in loop, and wool if the budget allows and the room is not a mudroom. Solution-dyed means the colour is in the molten fibre before it is extruded rather than applied afterwards, so it cannot bleach out — it is worth asking about specifically for sun-facing rooms and for households that clean with peroxide products.

Pile construction and the numbers on the spec sheet

Two carpets in the same fibre can perform completely differently depending on how the yarn is twisted and how densely it is tufted. Ask for these three numbers, which are on every manufacturer's specification sheet even when they are not on the showroom tag:

• Face weight — ounces of pile yarn per square yard. Typical residential runs 30–60 oz. Useful, but meaningless on its own, because the same yarn can be piled high and loose or short and tight.
• Pile height — in inches. Shorter almost always wears better.
• Density — the industry formula is face weight × 36 ÷ pile height. This is the number that predicts matting. Below about 2,000 is builder-grade; 3,000–4,000 is solid residential; above 5,000 is premium. A 50 oz carpet at a ½-inch pile height has a density of 3,600; the same 50 oz at ¾ inch is only 2,400, and it will lie down in the traffic lane far sooner.

A fourth number matters for cut pile specifically: twist level, the turns per inch in the yarn. Five or more turns per inch, heat-set to hold, is what stops a cut pile from untwisting into a fuzzy, blotchy "traffic lane" look. Frieze carpets are defined by their very high twist, which is exactly why they hide footprints.

Don't forget the pad

Carpet pad is a separate purchase. Match the carpet's square yardage 1:1. Better pad ($1–2 more per sq yd) extends carpet life by years; cheap pad shows wear patterns through the carpet within 18 months. It is also the cheapest upgrade in the whole job — the difference between the minimum acceptable pad and a good one on a bedroom is typically less than the cost of a single roll of carpet.

Two specification numbers matter, and thicker is emphatically not better. Thickness is limited because a pad that is too soft lets the carpet backing flex under every footstep, which fatigues and eventually delaminates it. Density, in pounds per cubic foot, is what actually supports the carpet. Most manufacturers' warranties specify a maximum thickness of 7/16 inch and a minimum density of 6 lb for cut pile, and installing outside those limits can void the warranty — worth checking the specific product's requirement before you buy.

Berber and other loop carpets are the important exception to "comfort equals thickness": they need a thinner, firmer pad, typically 3/8 inch at 8 lb or a fibre pad, because a soft pad lets the loop backing flex and the rows separate.

Worked example: a 14 × 12-ft bedroom

The room is 14 × 12 = 168 sq ft. A 10% waste factor gives 184.8 sq ft, and dividing by 9 converts that to 20.5 sq yd, which rounds up to 21 sq yd of carpet and 21 sq yd of pad. Raw, unwasted area is 168 ÷ 9 = 18.7 sq yd, so the waste factor is costing you about two and a quarter yards — one strip of trim along each wall, essentially.

From a 12-ft roll, the installer cuts a drop about 14 ft 6 in long (the 14-ft room dimension plus trim allowance) at the full 12-ft width. That is 174 sq ft, or 19.3 sq yd of roll goods, but you will be billed in running feet and the shop will round the drop up — so an order of 21 sq yd is the right number to walk in with. Note that a room measuring a true 12 ft across cannot be covered edge-to-edge by one 12-ft drop once the selvage is trimmed, so expect a narrow fill strip along one wall, seamed and nap-aligned with the field.

Worked example: a 13 × 20-ft family room, and why roll width is the real cost

The calculator's arithmetic: 13 × 20 = 260 sq ft, plus 10% is 286 sq ft, ÷ 9 = 31.8 → 32 sq yd of carpet and 32 sq yd of pad. That is the area you need to cover, and for the pad it is the correct number, because pad comes in wide rolls and is trimmed freely.

The carpet is a different story, because it has to come out of a fixed-width roll with all the nap running the same way. Off a 15-ft roll, the 13-ft dimension fits, so the installer takes one continuous 20-ft drop: 15 × 20 = 300 sq ft, or 33.3 sq yd. That is within a yard and a half of the calculator's 32, and there are no seams at all.

Off a 12-ft roll, the room is a foot too wide. You get a 12 × 20-ft field piece (240 sq ft) and still need a strip roughly 13 inches wide by 20 ft long to finish. That fill strip has to run in the same nap direction as the field, so it cannot be cut sideways from the leftover — it has to come off a second 20-ft drop. Total goods: 40 running feet × 12 ft = 480 sq ft, or 53.3 sq yd, of which you use 260. That is not a mistake by the shop; it is the geometry. Which is why, on any room between 12 and 15 feet across, the first question to ask is whether your chosen carpet is made in a 15-foot width. It very often changes the total cost more than the grade of carpet does.

Stairs are quoted separately, and they are not cheap

This calculator sizes rooms, not staircases. Geometrically, one step consumes about 1.5 linear feet of carpet — roughly 10–11 inches of tread, 7–8 inches of riser, and a wrap over the nosing — so a 36-inch-wide stair is about 4.5 to 5 sq ft, or half a square yard, per step. In practice installers budget closer to a full square yard per step once nap direction, roll-width cutting, and the pieces lost at landings are accounted for. A typical 13-step flight is therefore an 8 to 13 sq yd order on its own.

Labour is where stairs really bite: a stair costs several times more per step to install than the equivalent area of open floor, and a cap-and-band (upholstered) finish costs considerably more than a waterfall wrap. Use a high-density pad on stairs — it is the highest-wear surface in the house — and use a cut pile with a high twist or a level loop, not a soft plush.

Installation: why carpets ripple

Stretch-in carpet is held by tackless strip around the perimeter and is meant to be installed under real tension using a power stretcher, a long lever tool that braces against the opposite wall. The industry installation standard for residential stretch-in work calls for power stretching; a knee kicker alone is for positioning and for small areas, not for stretching a room. Rippling and buckling a year or two after installation is, in the great majority of cases, an under-stretched installation rather than a defective carpet — and it is a warranty exclusion with most manufacturers.

Two more things good installers do. They condition the carpet, letting it acclimate in the room for a day or so, and they stretch on a warm day or with the heat on, because carpet stretches more readily when it is warm. And they plan seams deliberately: running the length of the room rather than across it, away from doorways, out of the main traffic path, and parallel to the main light source so that light rakes along the seam rather than across it. Seams are always visible under close inspection; a well-placed one is simply never inspected closely.

When to call a pro

Almost always, for stretch-in carpet. The power stretcher, seaming iron, and knee kicker are specialist tools, seaming is genuinely skilled work, and a botched stretch shows up as ripples months later when the retailer has moved on. Stairs in particular are a skill job. Carpet tiles and a simple glue-down in a square basement room are reasonable DIY projects; a seamed, stretched living room is not. If you are getting quotes, ask specifically whether the price includes power stretching, removal and disposal of the old carpet and pad, and moving furniture — those three line items are where quotes diverge most.

Frequently asked questions

Considering hard-surface flooring instead? Compare in the hardwood vs laminate comparison or use the flooring calculator.