Carpet Calculator
Find out how many square yards of carpet and padding you need to buy for a room.
Room dimensions
Results
For a 15 ft × 12 ft room on a 12 ft wide roll, you'll need about 20.3 sq yd of carpet (1 strip) plus about 20 sq yd of padding.
Carpet needed
20.3 sq yd
That's a typical amount for a standard living room or a couple of connected bedrooms.
Confirm seam placement and pile direction with your installer before the order is cut — at this size, you're likely looking at at least one seam, and where it falls matters for how visible it is.
Padding needed: 20 sq yd
Room floor area: 20 sq yd
Roll strips required: 1
How this works
Because broadloom carpet comes off a fixed-width roll and can only be cut straight across that width, this calculator computes material two ways — once assuming the room's length runs along the roll (and its width runs across it), and once with the two swapped — and picks whichever orientation needs less material, the way an experienced installer would choose. For the chosen orientation, the number of full-width roll strips needed is the room's across-the-roll dimension divided by the roll width, rounded up to a whole strip (a partial strip still needs a full width of material). Each strip's length is the room's along-the-roll dimension plus a fixed seam/trim allowance, and the total material is strip count x roll width x strip length. An optional pattern-waste percentage is then applied on top, for carpet with a repeating design that needs to align across seams. Padding is reported separately at the room's plain bare-area figure, since padding is typically cut to the room's shape directly and isn't subject to the same roll-width constraint as the carpet itself. All figures are converted to square yards for display, matching how US carpet retailers conventionally price and quote the material. The orientation-picking step matters more than it might first appear: because strip count is a step function of the across-the-roll dimension (a room needs exactly 1, 2, or 3 strips, never 1.4), small differences in which dimension runs across the roll can produce a materially different total even for the same room. This calculator always evaluates both orientations rather than assuming length always runs one particular way, because assuming a fixed orientation would sometimes force an extra unnecessary strip and seam. The seam/trim allowance is applied once per strip's length regardless of how many strips the room needs, on the assumption that each strip is trimmed individually at install time — this is a simplification that holds well for typical rectangular rooms but undercounts trim allowance slightly for rooms needing unusual cuts around bump-outs or fireplace hearths (see the edge cases above). This calculator does not attempt to model the labor cost or time difference between a one-strip and a multi-strip installation, only the material quantity difference; ask your installer separately about labor cost implications of a seamed versus seamless install, since seaming typically adds installation time independent of material cost. If your room's shape doesn't map cleanly onto a single rectangle — an L-shape, a bay window alcove, or a room opening into a hallway — split it into rectangles as described in the edge cases above and get a professional measure to confirm seam placement across the combined shape, since this calculator's per-rectangle outputs don't automatically account for how strips from adjoining rectangles might be combined to reduce total seams. Standard roll width (12 ft) and seam-allowance guidance: Lowe's and The Home Depot carpet installation/measuring guides.
Worked example
A 12 ft x 15 ft bedroom, using standard 12 ft wide roll carpet with a 3 in seam allowance and no pattern waste: since the room's 12 ft dimension exactly matches the roll width, running the 15 ft dimension along the roll needs just one strip, cut 15.25 ft long (15 ft plus the 3 in trim allowance). That's 12 ft x 15.25 ft = 183 sq ft of carpet, or about 20.3 sq yd once converted (183 / 9). The room's bare floor area is 180 sq ft (20 sq yd) — padding is estimated at that smaller, roll-unconstrained figure, so you'd order roughly 20.3 sq yd of carpet and about 20 sq yd of padding.
A second example: a wider room needing a seam
A 20 ft x 20 ft family room on the same 12 ft roll: neither the room's length nor width fits within a single 12 ft strip, so at least two strips are required. Running strips across the 20 ft width needs 2 strips (12 ft roll covers up to 24 ft of width in two strips), each cut 20.25 ft long (20 ft plus the 3 in allowance) — total material is 2 x 12 ft x 20.25 ft = 486 sq ft, or 54 sq yd. Compare that to the room's bare 400 sq ft (44.4 sq yd) floor area: the roll-width constraint alone adds roughly 9.6 sq yd, or about 22% more material than the bare-area figure would suggest — a jump that a naive length-times-width estimate would miss entirely.
Common mistakes
Calculating carpet the same way as tile or paint (bare area only)
Multiplying length by width and treating that as the amount of carpet to buy. Carpet's roll-width constraint means this consistently underestimates the true amount needed, sometimes significantly, because it ignores strip waste and seam allowances entirely.
Not checking which roll widths are actually in stock for the chosen style
Assuming every carpet style comes in every roll width (12ft, 13'2", 15ft). Many styles are only milled in one width. Confirm the actual roll width your specific chosen product ships in before finalizing a strip-count estimate, since using the wrong roll width in the calculator will give you a materially wrong answer.
Ignoring pile direction when combining multiple strips
Carpet pile has a directional nap — light reflects differently depending on which way you look along it. If a room needs multiple strips, all strips must run the same direction, or the seam becomes highly visible even if the color matches perfectly. This isn't a material-quantity issue, but it affects how the strips this calculator outputs actually get cut and laid.
Forgetting stairs need a completely different measurement method
Carpeted stairs are measured per step (tread depth + riser height, times number of steps, plus wrap allowance), not as a length x width rectangle — this calculator models flat rooms only. Get a separate stair-specific measurement from your installer rather than trying to fold stair yardage into a room calculation.
Buying padding at the same quantity as the carpet's roll-fitted figure
Padding doesn't have carpet's roll-width constraint (it's typically sold in wide rolls and cut to the room's actual shape), so ordering padding at the same inflated square-yard figure as the carpet itself over-buys padding. This calculator reports padding separately at the room's bare area for that reason.
Not accounting for closet or alcove seams separately
Assuming a closet inside a carpeted room is automatically covered by the main room's strips. Depending on the closet's position relative to where strips fall, it may need its own small seam and offcut — flag closets and alcoves to your installer rather than assuming the main-room estimate silently includes them.
Entering room dimensions rounded to the nearest foot
Rounding a 12ft 4in wall down to 12ft to make data entry easier. On a roll-width-constrained material, a few extra inches on the across-the-roll dimension can be the difference between fitting in one strip and needing a second — measure to the nearest half-inch and enter the precise figure, since carpet's step-function strip math is far less forgiving of rounding than a simple area calculation would be.
Assuming the cheapest roll width is always the best choice
Choosing whichever roll width your retailer quotes first without checking whether a different available width would eliminate a seam entirely for your room's dimensions. A wider roll sometimes costs more per square yard but needs a smaller total quantity and avoids a seam — run this calculator with each roll width your retailer actually stocks for the style you want, and compare total cost, not just quantity.
When this calculator's model stops applying
- Stairs and stair landings: measured per step, not as a room rectangle — see Common Mistakes above. Do not attempt to convert a stair's total surface area into this calculator's length/width inputs.
- Rooms with more than four sides, or significant bump-outs (bay windows, angled walls): this calculator models a single rectangle. For an irregular room, split it into rectangles, run the calculator once per rectangle, and note that strip orientation may need to differ between sections — get an installer's opinion on seam placement across the whole irregular shape rather than combining this calculator's per-rectangle outputs blindly.
- Carpet tile (modular carpet squares) instead of broadloom roll carpet: carpet tile doesn't have a roll-width constraint at all — it's ordered by area plus a much smaller waste factor, closer to this site's tile calculator's model than this one. Don't use this calculator for a carpet tile order.
- Very large open areas (over roughly 300-400 sq ft) needing 3+ strips: at this scale, seam count and placement become a bigger design decision than a pure material-quantity one — get a professional measure before ordering, since installer preferences about where seams fall (and whether to special-order a wider roll to reduce seam count) can change the material total more than this calculator's model captures.
- Carpet requiring pattern match at seams with a large repeat distance (over roughly 12-18in): the pattern-waste percentage field handles small to moderate repeats reasonably, but very large repeat patterns can require substantially more waste than typical percentage guidance suggests — get a repeat-specific waste figure from the retailer for large-repeat patterned carpet.
- Rooms requiring transition strips or thresholds where carpet meets another flooring type: this calculator estimates carpet and padding material only, not transition hardware, which is typically bought separately by linear foot of doorway or edge.
- Rooms with a fireplace hearth, built-in cabinetry, or other permanent floor obstruction: this calculator treats the room as a clear rectangle. A raised hearth or built-in reduces the actual carpet needed but also disrupts strip layout in a way that's hard to generalize — get a professional measure for rooms with substantial permanent obstructions rather than trying to net out the obstruction's area yourself.
- Carpet runners and area-rug-style installations (not wall-to-wall): this calculator assumes a full wall-to-wall installation using the room's own dimensions as the coverage target. A runner or bound area rug is ordered to its own fixed finished size from a rug retailer, not calculated from room dimensions with a roll-width and seam model.
FAQ
Why is the carpet needed more than my room's actual square footage?
Carpet comes off a roll of fixed width — typically 12 feet — and can only be cut straight across that roll, not freely shaped like tile or paint coverage. If your room's narrower dimension doesn't divide evenly into the roll width, you either waste the leftover strip width or need a seam, and every cut strip is made slightly longer than the room to allow for trimming. Both effects mean the carpet you buy is almost always somewhat more than your room's bare floor area.
Why does this calculator try both room orientations?
Which room dimension you run across the roll's width matters a lot. A 12ft x 20ft room run one way might fit in a single 12ft-wide strip with no seam; run the other way, it needs two strips side by side with a visible seam and more leftover waste. This calculator checks both orientations and picks whichever needs less material, which is exactly what an experienced installer would do.
Is carpet really sold by the square yard, not the square foot?
Yes — US carpet retailers conventionally price and quote carpet by the square yard (9 sq ft), a holdover from when carpet was primarily sold in bolts measured that way. This calculator computes everything in square metres internally and converts to square yards for display, since that's the unit you'll see on a retailer's quote.
Do I need to buy padding separately, and how much?
In most residential installations, yes, padding is a separate line item from the carpet itself. Unlike carpet, padding is cut to fit the room's actual shape without roll-width waste, so this calculator estimates padding at the room's bare floor area rather than the inflated roll-fitted carpet figure — though it's still common to add a small buffer (a few percent) for trimming.
What if my carpet has a pattern that needs to match at the seams?
Patterned carpet (a repeating geometric design, as opposed to a plain or textured loop/cut pile) typically needs extra material so the pattern lines up across a seam, since each strip may need to be shifted to align the repeat. Use the pattern-waste field to add that extra percentage — ask your carpet retailer for the specific pattern-repeat waste they recommend for your chosen product, since it varies by pattern size.
Can I avoid a seam entirely?
Only if your room's narrower dimension is less than or equal to the roll width you're using (commonly 12 ft, sometimes 13'2" or 15 ft from certain mills). For anything wider, a seam is unavoidable with broadloom carpet — the only way to avoid seams on a larger room is carpet tile, which this calculator doesn't model.
Where should a seam be placed if one is unavoidable?
Installers generally try to place seams in low-traffic areas, away from doorways, and running with the direction of light from windows rather than across it, since a seam is more visible when light rakes across it perpendicular to the seam line. This calculator tells you how many strips and roughly how much material you need, but exact seam placement is a judgment call best made by whoever installs it, looking at your specific room.
Does closet space count as part of the room for this calculation?
If you're carpeting the closet floor too, include its length and width by treating it as a separate rectangle and running the calculator again, then adding results — don't just pad your main room's dimensions to guess at the extra. Closets are often carpeted with leftover material from the main room's cut strips rather than ordered separately, so check with your installer before buying extra just for a closet.
Why did my result change a lot when I switched roll width?
Roll width directly determines how many strips your room needs, and the number of strips is a step function, not a smooth one — going from a roll width that requires 1 strip to one that requires 2 (or vice versa) can change total material by a large jump, even though the room itself didn't change size. If two different roll widths give very different quotes, that's expected and worth asking your retailer which widths they actually stock for your chosen carpet style.
How much should I budget above this calculator's estimate?
This calculator already includes a standard seam/trim allowance per strip. Beyond that, it's common practice to round the final square-yard order up to the nearest whole or half yard the retailer sells in, and to ask your installer directly whether they want additional buffer for your specific room's fit (stairs, closets, and irregular shapes typically need more).
Does carpet fiber type (nylon, polyester, wool) change how much I need?
No — fiber type affects durability, feel, and price per square yard, not the quantity of material needed for a given room. The roll-width and seam-allowance math in this calculator applies the same way regardless of fiber, since it's driven by the physical roll dimensions carpet is manufactured and shipped in, not by what the carpet is made from.
What's the difference between broadloom and carpet tile, and does this calculator handle both?
Broadloom is carpet sold off a continuous roll of fixed width, which is what this calculator models. Carpet tile (also called modular carpet) comes in individual squares, typically 18in-24in per side, ordered by area with a much smaller waste allowance similar to floor tile, and installed without the roll-width or seam-orientation constraints this calculator accounts for. If you're using carpet tile, use this site's tile calculator instead, or ask your retailer for their per-square coverage figures.
Why does the calculator ask for room dimensions in feet rather than just square footage?
Because carpet's roll-width constraint depends on which specific dimension runs across the roll, not just on total area — two rooms with identical square footage but different length-to-width ratios can need very different amounts of carpet. A single square-footage number would lose the information needed to figure out strip count and orientation, which is why this calculator (unlike the tile or paint calculators) needs both dimensions entered separately.
Related tools
Tile Calculatorcomparing a carpeted room against a hard-surface option, or estimating a mixed-flooring project with both carpet and tile areas.Flooring Calculatorcomparing carpet against laminate, hardwood, or vinyl plank for the same room before you settle on a material.More flooring tools (underlayment calculator) are planned but not yet published.