Carpet and Vinyl Roll Calculator: Drops, Seams and Roll Length

What it calculates

For a rectangular room covered in broadloom carpet or sheet vinyl from a roll, the calculator gives:

• the number of drops (full-length pieces) across the room;
• the drop length, with trim and any pattern allowance;
• the roll length to order, in running metres;
• the area ordered against the room area, and the offcut as a share of it;
• the number of seams.

It also shows the same figures for the other lay direction, so the two can be compared. For carpet tiles, vinyl planks or tiles, use the flooring quantity calculator, which counts pieces and boxes.

Inputs

Room length and width are in metres; the equivalent in feet is shown under each.

Product chooses broadloom carpet or sheet vinyl. It only sets a starting roll width, 4 m for carpet and 2 m for vinyl, which you can change.

Lay direction sets whether the drops run along the room length or along its width.

The assumptions panel holds the roll width, the trim allowance at each end of a drop, the pattern match allowance and the wastage on the roll length.

Method

1. Across = the room dimension the drops are laid side by side across; run = the other one.
2. Drops = across ÷ roll width, rounded up.
3. Drop length = run + 2 × trim + pattern allowance.
4. Roll length = drops × drop length × (1 + wastage), rounded up to the next 0.1 m.
5. Area ordered = roll length × roll width.
6. Offcut = (area ordered − room area) ÷ area ordered.
7. Seams = drops − 1.

Assumptions

Limitations

• Rectangular rooms only. Split an L-shaped room into rectangles, or plan the drops on a drawing.
• Offcuts are not reused. In practice a wide offcut can sometimes fill a corridor or a recess; the calculator counts every drop as cut fresh from the roll.
• Bays, columns and doorway extensions are not included. Add their area as extra drops or extend the run.
• One roll is assumed. Large rooms may need more than one roll, and drops from different batches should not sit side by side; order enough from one batch.
• Underlay, adhesive, gripper, seam welding rod and subfloor preparation follow the manufacturer's instructions and are not counted.

Worked example

An 8 × 6 m room (26.2 × 19.7 ft) in broadloom carpet from a 4 m roll, drops along the 8 m length, 0.1 m trim at each end, no pattern and 3% wastage:

The room needs 16.9 m of 4 m wide carpet in 2 drops, with one seam. The second drop is cut down to 2 m wide, which is where the 29% offcut comes from. Laying the drops along the 6 m width instead gives 2 drops of 6.2 m, 12.8 m of roll (51.2 m²) and about 6% offcut. The same room in 2 m sheet vinyl along the length needs 3 drops, 25.4 m of roll and 2 seams.

How engineers use it

On a fit-out the floor finish is shown on a finishes layout, and the flooring contractor prepares a seaming or cutting plan for each roll product. The plan places the drops so seams avoid doorways, main routes and points where light rakes across the floor, keeps the pile or pattern running one way, and nests offcuts into corridors and recesses. The order comes from that plan, in whole running metres per batch.

When a professional design must replace it

Use the calculator to check how much roll a room needs or to compare lay directions. Replace it with a cutting plan from the flooring contractor before ordering, and wherever the room is irregular, the product is patterned, several rooms share one roll, or seam positions matter. Subfloor preparation and moisture testing follow the manufacturer's instructions for the product chosen.