Flooring
Laying Carpet and Carpet Tile
Broadloom arrives at a fixed width, so seam placement — not room area — drives every carpet and carpet-tile decision on site.
Published · Last reviewed
The Width You Are Given
Broadloom leaves the loom at a width you cannot change: 12 ft across most of North America, 4 m (13 ft 2 in) in metric markets, with 15 ft goods and narrower runner widths available in some qualities. Length is the quantity you buy; width is the constraint you inherit. Any room dimension larger than that width will carry a seam, and any room narrower than it produces fill that you either use elsewhere on the job or pay for as waste.
Measure the space both ways before deciding anything else. A 13 ft 6 in living room off 12 ft goods can be run with one seam and an 18 in fill strip, or turned ninety degrees and run as two drops with a shorter seam — different lineal quantities, different seam length, different visibility from the door. Take the wall-to-wall figure at several points; walls are rarely parallel, and the widest reading governs the cut.
Where a wider quality exists in the same style and colour, the arithmetic of one extra roll width often beats the labour and the risk of a seam across an open floor. Where it does not, accept the seam early and design the room around it, rather than discovering it at the tailgate with the roll already on the deck.
Where a Seam May Land, and Where It May Not
Daylight raking across a floor exaggerates any change of pile height or direction. Run seams away from the main window rather than across the line of light, so the eye follows the seam into shadow instead of tracking along its lit side. Loop and low-profile commercial goods reveal seams far more readily than a dense cut pile, and a Berber-style loop punishes a careless one for the life of the floor.
Traffic direction matters as much as light. A seam crossed at right angles by everyone entering the room takes repeated shear and eventually opens; a seam running with the walking line survives. Doorways, the pivot at the foot of a stair, and the swing arc of a desk chair are the three places a seam should never fall — hold it back beyond the casing, into the quieter part of the room.
Two further constraints tighten the plan. Keep seams out of the first few inches next to a wall, where tension is highest and the tape has least support behind it. And keep the total seam count to the minimum the roll width allows: every extra seam is another length of tape, another sealed edge, another chance for the installation to announce itself under a low winter sun.
Turning the Seam Plan Into Drops
With the seam lines settled, the roll becomes a list of drops. Each drop is the room length in the chosen direction plus trim allowance at both ends — enough to reach the tackless strip and be tucked, plus margin for walls that are out of square. Closets, bay returns and hearth cut-outs are either separate drops or extensions of an existing one, and every last one belongs on the same sheet, because the roll gets cut once.
Patterned goods change the arithmetic. Every drop after the first has to gain a full pattern repeat so the design can be slid into match at the seam, and that allowance is added per drop, not once per room. Down a long corridor the repeats alone can add a substantial length; on a large-scale pattern they can decide whether the space should be broadloom at all.
Nap direction has to stay consistent across every drop, which sometimes forbids the more economical nesting of cuts. Confirm too whether the material comes off a full roll or a short one: a remnant that cannot yield the longest drop forces the whole plan to be re-cut, usually with an extra seam nobody wanted.
Before the roll is cut, the seam plan you have just drawn has to become a lineal quantity — drops, trim allowance, pattern repeat and offcut — and that is the number this calculator returns.
The standard allowance most suppliers and estimating guides assume for ordinary work.
Carpet roll length needed
20.2 ft
Rooms wider than the roll width require seaming, which adds waste beyond this base estimate — for rooms requiring multiple carpet widths, consult an installer for exact seam placement and cut-length waste.
Running these inputs gives 20.2 ft as the carpet roll length needed. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States — pick a different market above and the figures re-cast accordingly.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Nap, Dye Lot and Side Match
Pile has a lay. Sweep a hand across a cut pile and it darkens one way and lightens the other; that difference is the entire reason drops must run in the same direction. A reversed drop reads as a colour change under any light, and once the adhesive has grabbed or the strip has taken the stretch it cannot be corrected without recutting.
Order in one dye lot and keep the roll numbers stapled to the plan. Where a job genuinely needs more than one lot, break the lots at a doorway or a change of room, never at a seam in an open floor. Side match — the slight variation between the two selvedges of the same roll — is normal and expected, which is one more argument for holding the seam count down.
Condition the material in the space before cutting anything. Carpet delivered cold and rolled tight behaves differently from carpet that has relaxed at service temperature and humidity; a cold backing will not take a seam iron predictably, and it will keep moving after the installer has gone home.
What Lies Under the Seam
A seam is only as flat as the substrate beneath it. Any high spot telegraphs through as a ridge along the tape, and any hollow lets the two edges lift independently under foot. Grind the ridges, fill the hollows with a patching compound compatible with the adhesive system, and remove old adhesive residue rather than bridging over it and hoping.
On concrete, test before the installation is even scheduled. ASTM F2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes, and ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride, are the two methods usually named in specifications. The acceptance limit belongs to the adhesive or flooring manufacturer, not to the test method itself. ASTM F710, Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring, is frequently written in alongside them for substrate preparation.
Timber substrates need the squeaks chased down and loose panels refastened first, with fastener heads set below the surface. Where a slab needs more than a skim coat to reach flatness tolerance, a poured levelling compound is the honest answer and it carries its own volume take-off; where a separate resilient or plank system shares the floor, its underlayment layer is a separate order entirely.
Building the Seam So It Holds
Trim both edges before joining them. A row cutter follows the line between rows on a cut pile; loop pile is cut from the back against a straight edge, one row in from the selvedge, so no half-tuft is left to shed. Seal every cut edge — latex seam sealer along the backing edge is required by the installation standards, not a finishing nicety.
Hot-melt tape under a heated iron remains the common method for stretch-in work. Set the iron to the tape manufacturer's stated temperature, move at a steady pace, and follow immediately with weights or a seam tractor so the backing seats while the adhesive is still open. An iron rushed leaves cold spots that release months later; an iron dwelt on glazes the tape and destroys its grab.
Judge the finished seam by feel before moving on. The two edges should meet with no visible gap and no compression ridge — forced together it peaks, left short it opens. CRI 104, Standard for Installation of Commercial Carpet, and CRI 105, Standard for Installation of Residential Carpet, describe the workmanship most North American specifications reference; in the UK, BS 5325, Installation of textile floor coverings — Code of practice, covers the same ground.
Tension Across the Seam, or None At All
Stretch-in carpet over cushion carries tension straight across the seam, so the seam is made before the final stretch and the stretch has to be genuine. A power stretcher, not a knee kicker alone, is what the installation standards call for in any room of consequence. Under-stretched carpet ripples once the heating comes on, and those ripples migrate to the seam and lift it.
Direct glue-down transfers nothing across the joint — each side is held independently by the adhesive — but it is far less forgiving about open time. Spread with the notch the adhesive data sheet specifies, respect its working window at the real room temperature rather than the one on the drawing, and roll with the specified weight so the backing is properly wetted out. Carpet laid into skinned adhesive lets go at the seam first.
Double-stick sits between the two: cushion bonded to the substrate, carpet bonded to the cushion, with the seams in each layer deliberately offset. Hold the cushion joints a clear distance away from the carpet joints, and confirm the building's HVAC is running at service conditions before a single pail is opened.
The Modular Answer: Seams Everywhere, On Purpose
Carpet tile inverts the whole problem. Rather than a few long seams hidden where light and traffic will not find them, the floor becomes nothing but seams on a regular grid — 50 cm or 24 in squares across most commercial ranges, with plank formats around 25 x 100 cm. Because every joint is identical, none of them reads as a defect, and a damaged tile lifts out and is replaced without disturbing anything around it.
Set the grid from control lines, never from a wall. Snap a centre line each way, adjust so the border cut lands at half a tile or more on opposing sides, and check the grid against the dominant sightline — a corridor, a glazed elevation, a run of workstations — because that is what the eye will use to decide whether the floor is square. Columns, floor boxes and demountable partition heads all want the grid arriving at them cleanly.
Installation direction is printed on the back of every tile and it is not advisory. Monolithic, quarter-turn, ashlar and brick layouts each consume a different amount of cut waste and each treats shading differently. Some ranges permit mixed dye lots and some forbid them outright; the manufacturer's instruction governs, and blending boxes across the floor is the standard defence against a lot change showing up as a block.
| Layout | Tile orientation | Effect on the finished floor |
|---|---|---|
| Monolithic | All arrows the same way | Most directional appearance; shows shading and lot variation most readily |
| Quarter-turn | Arrows rotated 90° tile to tile | Most forgiving of shading and minor lot variation; reads as a woven field |
| Ashlar / brick | Rows offset by half a tile or plank | Breaks up long joint lines; border cuts and waste differ on each axis |
| Non-directional / random | Mixed per manufacturer's instruction | Hides variation well but demands disciplined blending across boxes |
Once the grid direction and the border cut are settled, tile count, cut-tile allowance and box quantity all fall out of those two decisions — this calculator converts the layout into an order.
Waste is set to 7% by hand. Pick a tier above to replace it, or keep your own figure.
Carpet tiles needed
171 tiles
For the dimensions entered, expect a carpet tiles needed of 171. Set for United States. The market selector changes the units and the trade terminology; any standard behind the formula is cited under sources.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Edges, Thresholds and the Last Cut
Every free edge needs a defined end. Tackless strip takes the stretch at walls; a metal or vinyl trim carries a change of level at a doorway; a capping strip closes carpet against a hard floor. The accessibility standard in force limits pile height and controls the profile of transitions on an accessible route, and the building code plus the local authority decide which standard applies — settle that before selecting trim, not after it is fixed.
Fire performance belongs to the specification rather than the installer's judgement. ASTM E648, Standard Test Method for Critical Radiant Flux of Floor-Covering Systems Using a Radiant Heat Energy Source, and its equivalent NFPA 253, sit behind the class that corridors and exit routes are usually required to meet; which class is required comes from the applicable building code for the occupancy.
Small details finish the job. Gripper set back from the wall by roughly the carpet thickness, cushion butted to the strip and not over it, the tuck line clean and continuous, and door undercuts checked against the finished thickness of carpet plus cushion instead of against a sample held to the frame.
Failures That Start at a Seam
Peaking — a raised line running the length of the joint — comes from edges forced together, from a seam made after the stretch was pulled, or from a ridge left in the substrate. Zippering, where the seam opens tuft by tuft, is almost always an unsealed or badly trimmed edge; it shows up weeks later under traffic and re-taping alone will not cure it.
Delamination along a seam points to adhesive that skinned before the carpet went in, an iron moved too fast, or a backing that never reached temperature. A visible tape line suggests over-application or a compressible patch underneath. Each of these has a distinct cause and each is diagnosed by lifting a short length and looking, not by arguing about it from the top side.
Movement is the slow failure. Loop goods take up and relax with humidity, and a stretch-in floor installed in cold, dry conditions will want re-stretching after the first heating season. Say so at handover, leave attic stock from the same dye lot, and record roll numbers and tile batch on the O&M documentation so a repair years out still matches the floor around it.
Before the roll is cut
Six checks that decide whether the seam plan survives contact with the floor.
- Roll width and dye lot confirmed — Verify the actual width, record roll numbers, and keep one lot across every drop in the same sightline.
- Seam plan drawn on paper — Fix every seam against light, traffic and door swings before any lineal quantity is ordered.
- Pattern repeat added per drop — A full repeat on each drop after the first; long corridors punish this omission hardest.
- Substrate moisture and flatness — In-situ RH or MVER on concrete against the adhesive maker's limit; grind and fill before tape goes down.
- Seam sealer and matched tape — Every cut edge sealed, with tape type and iron temperature taken from the manufacturer's figures.
- Attic stock and batch record — Spare broadloom or tiles from the same lot, with roll and batch numbers logged at handover.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.
Drawn from
- CRI 104 — Standard for Installation of Commercial Carpet
- CRI 105 — Standard for Installation of Residential Carpet
- BS 5325 — Installation of textile floor coverings — Code of practice
- ASTM F2170 — Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes
- ASTM F1869 — Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride
- ASTM F710 — Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring
- ASTM E648 — Standard Test Method for Critical Radiant Flux of Floor-Covering Systems Using a Radiant Heat Energy Source
- NFPA 253 — Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source
Guidance, not a specification. Local codes, the engineer of record and the product manufacturer’s instructions govern where they differ from anything written here.