Understanding your result
The headline names the recommended layout, with its strips, seams, roll length, carpet and offcut beneath it. The two stats summarise both options in seams and roll length, and the table describes each fully, followed by where the seam would fall: with a full strip laid first from one wall, or with both strips trimmed equally so the seam sits in the middle.
The two options are strips along the long walls and strips across the room. The ranking is in order of importance: fewer seams first, because every seam is a weak point; then seams running toward the main light, worth up to a quarter of the room’s area in extra carpet; then a penalty for a fill strip under 2 ft wide; then less offcut. When the recommendation runs against the light because the other way would cost too much, the note says how much, so you can overrule it.
The seam position rows matter for the room you live in, not for the order. A full strip from the wall you see first puts the seam near the far wall; trimming both strips equally centres it, which is easier to hide under a rug or a bed. To order the carpet for the chosen layout, use the carpet calculator with the pile direction set; the same strip logic applies to roll goods on the sheet vinyl calculator, and the pad strips that go beneath at right angles are on the carpet padding calculator.
How we calculate this
The weights turn the installer’s priorities into arithmetic: a seam is never worth trading for carpet, a seam toward the light is worth a fair amount, and a skinny fill strip is to be avoided. They are judgements, written down so you can see them. The pile direction and seam guidance come from the Carpet and Rug Institute’s CRI 105 residential standard. The guide to carpet roll arithmetic covers the reasoning with diagrams, and the sheet vinyl guide applies the same thinking to vinyl.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Roll width | 12 ft (4 m) | The standard US broadloom width |
| Trim | 6 in per strip | Installer practice |
| Seams toward the light | worth up to 25% of the room area in carpet | A judgement based on CRI 105’s preference for seams in the direction of the light |
| Narrow fill strip | under 2 ft penalised | Installer practice; narrow strips are hard to stretch and seam |
| Room | 18 × 14 ft (5.5 × 4.3 m) | Chosen so the default needs a seam |
Assumptions last reviewed October 8, 2026.
The planner assumes a rectangular room with one main light source. A room with windows on two sides, or an L shape, has more options than two, and an installer’s cut plan on paper is the better tool there. It does not account for doorways, which can rule out a seam position, or for furniture that will hide a seam. The carpet padding guide explains why the pad beneath a seam matters for how long it lasts.
Two worked examples
A 20 × 15 ft living room, window on an end wall
12 ft roll.
- Along the long walls: 2 strips of 20.5 ft, 41 ft of roll, 1 seam, offcut 192 sq ft
- Across the room: 2 strips of 15.5 ft, 31 ft of roll, 1 seam, offcut 72 sq ft
- Both have one seam. Running toward the window costs 120 sq ft more, over the 75 sq ft the light is worth here, so: strips across the room
- Seam: centred, 10 ft from either end wall, or 12 ft from the starting wall with an 8 ft fill strip
The planner recommends the cheaper layout but tells you what the other costs: 120 sq ft, about 13 sq yd. In a living room where the seam will be in full view from the sofa, many people pay it.
A 16 × 13 ft bedroom on a 13.5 ft roll, window on a side wall
- Along the long walls: 13 ÷ 13.5 → 1 strip of 16.5 ft, no seam, offcut 15 sq ft
- Across the room: 16 ÷ 13.5 → 2 strips of 13.5 ft, 1 seam, offcut 157 sq ft
- Recommendation: one piece along the long walls
A seam beats nothing, whatever the light. On a 12 ft roll the same room needs a seam either way; this is the case where a wider roll pays for itself.
Where to find your inputs
Room. Wall to wall at the widest points. The planner always treats the longer dimension as the length.
Roll width. The widths the chosen carpet is made in, from the product page or the dealer.
Main light. The wall with the largest window, or the doorway most people see the room from if there is no strong window.
Pattern repeat. From the product page; plain carpet has none.
Common mistakes
- Letting the cheapest layout decide alone. A seam across the light in a living room is visible every afternoon.
- A seam in a doorway. Never, under any layout.
- A fill strip a foot wide. It is hard to stretch and pulls away. Centre the seam instead.
- Forgetting the pad seam. It must not sit under the carpet seam.
- Ignoring the wider roll. A room just over 12 ft may need no seam on 13.5 or 15 ft.
- Mixed pile directions. Every piece runs the same way, whatever the seam plan.
Questions people ask
- Where should a carpet seam go?
- Running toward the main source of light, away from doorways, out of the main traffic lane, and ideally where furniture or a rug will cover it. The Carpet and Rug Institute's residential standard says seams should run in the direction of the light where possible and never across a doorway.
- Is it better to have the seam in the middle of the room or near a wall?
- Near a wall it is out of the traffic, but a last strip under about 2 ft wide is weak and hard to stretch. In the middle, with both strips trimmed equally, it is easier to install and can sit under a rug or a bed. Either is fine if the seam is well made; neither belongs in a doorway.
- Why does the seam show in some light?
- Light crossing a seam catches the slight difference in pile height and direction on each side, so the seam reads as a line. Light running along the seam shows it much less. That is why the direction of the main window decides which way installers want to run the roll.
- Will a wider roll avoid the seam?
- If the room is narrower than the roll in one direction, yes. A 13 × 16 ft room needs a seam on a 12 ft roll but none on a 13.5 ft roll. Not every carpet is made in the wider widths, so check before you choose the style.
- How much extra carpet does a better seam cost?
- It depends on the room. In a 20 × 15 ft room on a 12 ft roll, running the seams toward an end window costs 120 sq ft more carpet than running them across. The planner shows the difference so you can weigh it.
- Does the pad seam matter too?
- Yes. Pad seams should run at right angles to the carpet seams, or at least 6 inches away from them, so the two never coincide and the carpet seam has firm support beneath it. The padding calculator lays the pad strips accordingly.