1 Material & roll details
Roll goods (carpet and sheet vinyl) are sold by the linear metre from a roll of fixed width. The roll width determines how many drops are needed — not the square metreage.
Flooring type
2 Pile / construction type
The pile type determines how seams must be made, whether rib cutting is possible, and how forgiving the join will be. This is critical for professional seam planning.
Carpet / material construction
Select the construction type — it affects seam technique and join visibility advice.
3 Room dimensions
Measure the longest dimension as the length. Width is the shorter or the direction the roll will be cut across.
m
m
mm
Default trim is 150 mm each end (300 mm total per drop). Increase for rooms with out-of-square walls or large skirtings.
4 Lay direction
This is the direction the carpet runs from the roll — pile direction for carpet, or grain direction for vinyl. It determines the number and length of drops. Critically affects total linear metres and seam positions.
Running direction
Drops run parallel to the length of the room. Roll is cut to room length. Number of drops = room width ÷ roll width (rounded up). Seams run lengthways.
5 Pattern matching
Pattern matching is the most critical and most frequently miscalculated part of roll goods estimation. Select the type that applies to your material.
Free match
No pattern. Plain, texture, or random weave. No repeat waste.
Straight match
Pattern rows align across seam. Each drop must start at same point in repeat.
Half drop
Even drops offset by ½ repeat. Most common on printed carpets and vinyl.
💡 Professional knowledge
⚠ Direction — this is not optional, it is absolute
No piece of carpet can be placed running in a different direction to any other piece in the same installation. This is not merely about seam visibility. The colour of the carpet changes when light hits a differently-oriented piece — even from the same roll, cut from the same batch, the piece laid in the opposite direction will appear a noticeably different shade. This is a fundamental optical property of how pile reflects light, and it applies to every carpet type: cut pile, loop pile, twist, plush, Axminster, Berber — without exception.
The pile direction is the machine direction of the roll (the direction the carpet was manufactured, which is also the length of the roll). All drops and all cut pieces must run in this same direction. If a layout cannot be achieved with all pieces running the same way, the carpet cannot be laid properly from that roll — a different layout or different room configuration must be used.
The pile direction is the machine direction of the roll (the direction the carpet was manufactured, which is also the length of the roll). All drops and all cut pieces must run in this same direction. If a layout cannot be achieved with all pieces running the same way, the carpet cannot be laid properly from that roll — a different layout or different room configuration must be used.
⚡ Cross joins in doorways — sometimes unavoidable
The standard rule is to avoid cross joins, but a top-level professional will tell you they cannot always be avoided — particularly in doorways. Several physical realities make this the case:
Roll size and weight: A full 12ft (3.66m) width of carpet, depending on the pile weight and backing, can be extremely heavy and unwieldy. Getting a full-width roll through a standard interior doorway (typically 820–870mm) is not always physically possible without damaging the carpet or scratching paintwork on the door frame. This is a real, practical constraint — not a failure of planning.
Doorway cross join technique: A top professional company will take accurate physical measurements of the entire floor plan and plan the cut layout on the cutting room floor before any carpet is put down. This allows them to plan drops where part of the roll runs through a doorway: the cut section from one room's drop "generally drops into the opposite side" — meaning the offcut from one room naturally becomes the piece needed for the adjacent room or hallway on the other side of the doorway. This minimises waste and keeps cross joins to their most defensible positions.
Cross join position matters: Where a cross join cannot be avoided, it should be placed in the doorway itself — specifically under the door where the door cover strip will conceal the join entirely. A cross join hidden under a door strip is invisible. A cross join in the middle of a visible floor is unacceptable.
Roll size and weight: A full 12ft (3.66m) width of carpet, depending on the pile weight and backing, can be extremely heavy and unwieldy. Getting a full-width roll through a standard interior doorway (typically 820–870mm) is not always physically possible without damaging the carpet or scratching paintwork on the door frame. This is a real, practical constraint — not a failure of planning.
Doorway cross join technique: A top professional company will take accurate physical measurements of the entire floor plan and plan the cut layout on the cutting room floor before any carpet is put down. This allows them to plan drops where part of the roll runs through a doorway: the cut section from one room's drop "generally drops into the opposite side" — meaning the offcut from one room naturally becomes the piece needed for the adjacent room or hallway on the other side of the doorway. This minimises waste and keeps cross joins to their most defensible positions.
Cross join position matters: Where a cross join cannot be avoided, it should be placed in the doorway itself — specifically under the door where the door cover strip will conceal the join entirely. A cross join hidden under a door strip is invisible. A cross join in the middle of a visible floor is unacceptable.
Cross join rules by pile type — not all carpet is equal
Twist pile and plush pile (cut pile): Cross joins are less of a problem. The cut pile lies in a consistent direction and a well-made cross join with a seaming iron and tape can produce an acceptable result, particularly if the joint falls under a door strip or in a low-visibility position. Not ideal, but professionally acceptable when unavoidable.
Loop pile (Berber, commercial loop, structured loop): Avoid cross joins wherever physically possible. The loop structure creates a more visible edge at any cut, and the rib pattern of a loop carpet makes a cross join significantly more visible than a running join. However — as noted above — physical constraints in doorways may make a cross join unavoidable. When it cannot be avoided, a cross join on loop pile should be positioned under a door cover strip without exception.
Woven carpet — Axminster and Wilton: Apply the strictest standard. Axminster and Wilton are woven rather than tufted, meaning the pattern is integral to the weave. A cross join on a woven carpet disrupts the weave pattern, the pile direction, and the surface texture simultaneously. Avoid with every planning option available. When a cross join on a woven carpet truly cannot be avoided, it should be placed where it will never be seen — under a fixed piece of furniture, under a door strip, or in a concealed alcove.
Loop pile (Berber, commercial loop, structured loop): Avoid cross joins wherever physically possible. The loop structure creates a more visible edge at any cut, and the rib pattern of a loop carpet makes a cross join significantly more visible than a running join. However — as noted above — physical constraints in doorways may make a cross join unavoidable. When it cannot be avoided, a cross join on loop pile should be positioned under a door cover strip without exception.
Woven carpet — Axminster and Wilton: Apply the strictest standard. Axminster and Wilton are woven rather than tufted, meaning the pattern is integral to the weave. A cross join on a woven carpet disrupts the weave pattern, the pile direction, and the surface texture simultaneously. Avoid with every planning option available. When a cross join on a woven carpet truly cannot be avoided, it should be placed where it will never be seen — under a fixed piece of furniture, under a door strip, or in a concealed alcove.
✓ The cutting room floor — professional layout planning
A top-level professional carpet company does not plan the cut layout in their head or on paper alone. They physically mark out the floor plan on the cutting room floor using chalk lines, then unroll the carpet over the plan. This allows them to:
• See exactly how drops fall relative to room dimensions and doorways
• Plan which offcut pieces from one drop fill adjacent areas without cross joins
• Identify where doorway cross joins are genuinely unavoidable vs where a different layout avoids them
• Confirm pattern repeat alignment before any cut is made
• Check that all pieces are running in the same pile direction before commitment
The cutting room floor is where the calculation becomes a physical plan. The numbers in this calculator give you the quantity and layout — the cutting room is where you validate it against reality.
• See exactly how drops fall relative to room dimensions and doorways
• Plan which offcut pieces from one drop fill adjacent areas without cross joins
• Identify where doorway cross joins are genuinely unavoidable vs where a different layout avoids them
• Confirm pattern repeat alignment before any cut is made
• Check that all pieces are running in the same pile direction before commitment
The cutting room floor is where the calculation becomes a physical plan. The numbers in this calculator give you the quantity and layout — the cutting room is where you validate it against reality.
🎞 Rib cutting on loop pile — the invisible seam technique
Loop pile carpets — Berber, commercial loop, flatweave, structured loop — are woven with a clear rib structure running along the length of the roll (the machine/pile direction). The selvage edge of the roll can be trimmed precisely by cutting down a rib channel.
How it is done: Identify a rib running parallel to the edge. Place a straight edge along the rib. Using a carpet knife or row cutter, cut firmly along the rib channel — you are cutting only through the backing (hessian, latex, or secondary backing). No carpet fibre is cut.
The result is a perfectly clean edge where the last complete row of loops terminates with uncut loops. When this edge is butted against the trimmed edge of the adjacent drop (also rib-cut), the loops from both pieces align rib-to-rib with no visible gap, no exposed cut fibre, and no fraying risk. The seaming tape bonds to two clean backing edges.
This technique applies only to running joins (side joins) — not to cross joins, where the edges are cut ends and no rib structure is available.
How it is done: Identify a rib running parallel to the edge. Place a straight edge along the rib. Using a carpet knife or row cutter, cut firmly along the rib channel — you are cutting only through the backing (hessian, latex, or secondary backing). No carpet fibre is cut.
The result is a perfectly clean edge where the last complete row of loops terminates with uncut loops. When this edge is butted against the trimmed edge of the adjacent drop (also rib-cut), the loops from both pieces align rib-to-rib with no visible gap, no exposed cut fibre, and no fraying risk. The seaming tape bonds to two clean backing edges.
This technique applies only to running joins (side joins) — not to cross joins, where the edges are cut ends and no rib structure is available.
Where should seams never be placed?
In open traffic areas mid-room — seams should be in the least visible, least trafficked position possible. At the top of stairs if carpet runs up them. Under furniture that moves — chairs being pulled out, table legs dragging. Perpendicular to natural light — seams running at right angles to a window create shadow lines. The exception: cross joins that cannot be avoided belong under door cover strips, not in the middle of the room.
Why calculate by linear metres instead of m²?
Because carpet is sold from a roll of fixed width (3.66m). When you need more than one drop, you always take from the full roll width — even if you only use 400mm of it. The waste on the wide strip is unavoidable. Only linear metres gives you the correct quantity to order. An m² calculation hides this entirely.
A cross join (also called a butt seam or end-to-end join) is where the cut end of one piece of carpet meets the cut end of another piece. These are the most visible seam type because both edges are cut, the fibres at the cut edge are exposed and stand differently to the surrounding pile, and the backing is visible if the seam opens even slightly under foot traffic. In cut pile carpets, a cross join is almost always visible. In loop pile, it is slightly better but still far inferior to a running join. Cross joins should never be planned into a layout if avoidable by changing the lay direction.
✓ Running joins / side joins — the professional seam
A running join or side join is where the long selvage edge of one drop meets the long selvage edge of the adjacent drop. Both edges run parallel to the roll direction (the machine direction of manufacture). This seam is inherently less visible because: the pile direction is continuous across the seam; light falls the same way on both sides; and crucially — on loop pile carpets, the rib structure can be used to create a perfectly clean edge without cutting a single fibre.
🎞 Rib cutting on loop pile — the invisible seam technique
Loop pile carpets — Berber, commercial loop, flatweave, structured loop — are woven with a clear rib structure running along the length of the roll (the machine/pile direction). The selvage edge of the roll can be trimmed precisely by cutting down a rib channel.
How it is done: Identify a rib running parallel to the edge. Place a straight edge along the rib. Using a carpet knife or row cutter, cut firmly along the rib channel — you are cutting only through the backing (hessian, latex, or secondary backing). No carpet fibre is cut.
The result is a perfectly clean edge where the last complete row of loops terminates with uncut loops. When this edge is butted against the trimmed edge of the adjacent drop (also rib-cut), the loops from both pieces align rib-to-rib with no visible gap, no exposed cut fibre, and no fraying risk. The seaming tape bonds to two clean backing edges.
This technique is the reason why a professionally laid loop pile carpet with running joins, laid by someone who understands rib cutting, can have seams that are genuinely invisible from normal standing height. A cross join on the same carpet, even done by the same installer, will always show.
How it is done: Identify a rib running parallel to the edge. Place a straight edge along the rib. Using a carpet knife or row cutter, cut firmly along the rib channel — you are cutting only through the backing (hessian, latex, or secondary backing). No carpet fibre is cut.
The result is a perfectly clean edge where the last complete row of loops terminates with uncut loops. When this edge is butted against the trimmed edge of the adjacent drop (also rib-cut), the loops from both pieces align rib-to-rib with no visible gap, no exposed cut fibre, and no fraying risk. The seaming tape bonds to two clean backing edges.
This technique is the reason why a professionally laid loop pile carpet with running joins, laid by someone who understands rib cutting, can have seams that are genuinely invisible from normal standing height. A cross join on the same carpet, even done by the same installer, will always show.
How does direction affect cross joins in a rectangular room?
In a simple rectangular room with parallel drops, you cannot produce a cross join — all joins are running joins by definition. Cross joins arise when: an L-shaped or irregular room requires a piece to be cut from the end of a drop and placed at 90°; an offcut is used rotated 90° to fill an alcove or bay; or a short room is filled by placing pieces end-to-end rather than running a full length. The calculator's direction analysis shows you the seam positions from each wall so you can judge whether they fall in doorways or high-traffic areas — two further reasons to choose one direction over another.
Cut pile — why rib cutting doesn't apply
Cut pile carpets (plush, saxony, velvet, frieze) do not have the same rib structure as loop pile. The tufts are cut at a defined height and the fibres extend above the backing individually. Trimming a cut pile edge will always cut fibres. The professional technique for cut pile seams uses a row cutter (a tool that splits between two rows of tufts rather than through them) and a seaming iron with hot-melt tape. Even with perfect technique, a cut pile seam is more visible than a loop pile rib-cut seam. This makes lay direction even more critical for cut pile — plan seams into the least visible location.
Where should seams never be placed?
Doorways — foot traffic crossing a seam repeatedly is the fastest way to cause separation. Under furniture that moves — chairs being pulled out, table legs dragging. At the top of stairs if carpet runs up them. In direct light paths — seams running perpendicular to natural light (from windows) show as shadow lines. Ideally, seams run parallel to the main light source. The direction comparison in this calculator shows you the seam position from each wall — check that position against your door and window plan.
Why calculate by linear metres instead of m²?
Because carpet and vinyl are sold from a roll of fixed width. When you need more than one drop, you always take from the full roll width — even if you only use 400mm of it. The waste on the wide strip is unavoidable. Only linear metres gives you the correct quantity to order. A room that is 4.5m wide with 3.66m roll carpet needs two drops — the second 0.84m wide — but you still pay for and take away the full 3.66m wide piece from the roll. An m² calculation hides this entirely.