What is a linear metre of carpet?

Broadloom carpet is sold by the linear (or broadloom) metre: one metre cut off the roll at the roll's full width, usually 3.66 m or 4 m. So a linear metre of 3.66 m carpet is 3.66 m².

Why is my carpet more than the room's area?

The roll comes in a fixed width, so the last drop is usually wider than the space left. That strip past the wall is offcut. The calculator draws it and picks the direction that wastes least.

Which way should the carpet run?

Pile should run the same way through the whole house, and seams should follow the main foot traffic, never across a hallway or doorway. If the cheapest direction puts a seam in the wrong place, force the other direction.

How much underlay and smooth edge do I need?

Underlay covers the floor area, so divide it by the roll size (for example 1.8 × 15 m = 27 m²) and round up. Smooth edge goes around the walls but not across doorways, in 1.2 m strips.

Free calculator

Carpet calculator

Carpet comes off a 3.66 m or 4 m roll and is sold by the linear metre. Drops = room width ÷ roll width, rounded up. Linear metres = drops × room length. Try both directions and buy the shorter.

Your job

Rooms

Length

Width

Doorways

Doorways: total width of openings with no smooth edge. L-shaped room? Add it as two rooms.

Roll and layout

Roll width

Carpet runs

Pile should run the same way through the house, and seams with the main foot traffic. Force a direction if the cheapest one puts a seam in the wrong place.

Trim per drop

Pattern repeat

Ask your installer what they add for trimming. Patterned carpet is cut to whole repeats so the pattern lines up.

Stairs

Steps

Stair width

Per step

Per step is tread + riser + the wrap over the nosing. Pieces are cut across the roll, so several steps come from one piece.

Underlay, edges and look

Underlay rolls

Smooth edge around the walls (1200 mm strips)

Colour

Optional

Your price per linear metre

Ask your carpet supplier. The greyed number is an example only and is never used in your result.

Striped carpet past the walls is offcut. The roll below is what you buy.

Carpet to buy

8.40lm

Linear metres off a 3.66 m roll

Floor area

21.00m²

1 room

Seams

Dashed on the drawing

Offcut

9.74m²

30.74 m² bought

Underlay

1rolls

1.8 × 15 m rolls

Smooth edge

16strips

18.40 m of 1.2 m strips

Quick estimate

6.31lm

Area + 10% ÷ roll width, for comparison

The working, with your numbers

1. Room 1 drops5.00 ÷ 3.66, rounded up= 2
2. Room 1 carpet2 × 4.20= 8.40 lm
3. Carpet bought8.40 × 3.66= 30.74 m²
4. Underlay21.00 ÷ 27.0, rounded up= 1 rolls
5. Smooth edge(perimeter − doorways) 18.40 ÷ 1.2, rounded up= 16 strips

Typed those measurements in by hand?MetreMate measures them straight off your PDF plans. Free to start.

The formula, in plain words

1Drops = the room's width across the roll ÷ roll width, rounded up. Each drop runs the full length of the room.
2Drop length = room length + any trim allowance, rounded up to a whole pattern repeat for patterned carpet.
3Linear metres = drops × drop length. Both directions are tried and the one that buys less carpet wins, then the one with fewer seams.
4Stairs: pieces are cut across the roll, so a piece holds roll width ÷ stair width steps. Pieces × (tread + riser + nosing).
5Underlay rolls = floor area ÷ roll area, rounded up. Smooth edge strips = (perimeter − doorways) ÷ 1.2 m, rounded up.

Worked example

A 5 × 4.2 m room on a 3.66 m roll, plain carpet, no trim allowance.

1.Along the 5 m length: 4.2 ÷ 3.66 = 2 drops × 5 m = 10 linear metres.
2.Along the 4.2 m width: 5 ÷ 3.66 = 2 drops × 4.2 m = 8.4 linear metres.
3.Buy the shorter: 8.4 linear metres, which is 8.4 × 3.66 = 30.74 m² for a 21 m² room.
4.An area-only estimate (21 m² + 10% ÷ 3.66) says 6.31 linear metres, which would leave you short.

Answer: 8.4 linear metres with one seam, running across the room.

How to measure it

Measure each room's length and width at the widest points, into doorways and robes.
Treat L-shaped rooms and hallways as separate rectangles.
Add the width of every doorway that won't get smooth edge.
For stairs, count the steps and measure the stair width and one tread + riser, plus the wrap over the nosing.

Where the numbers come from

Every default in the calculator is a number a supplier or manufacturer publishes. We list the source next to it so you can check.

What	Value	Source
Standard broadloom widths are 3.66 m and 4.0 m	3.66 m roll width	Carpet Institute of Australia, Technical Specification (Carpets146 v4) (checked 2026-09-30)
Wastage a retailer adds to an area-based quick estimate	10 %	Choices Flooring, flooring measurement and cost guide (checked 2026-09-30)
Underlay rolls 1.8 m wide, 10 m or 15 m long (8 m rolls also sold in stores)	1.8 m roll width	Dunlop Underlay, Carpetmate range (checked 2026-09-30)
Smooth edge (gripper) strip length	1.2 m per strip	Roberts Smoothedge Wood 1200 mm, product listing (checked 2026-09-30)

Manufacturers named here are the source of the number, not a recommendation. Confirm quantities with your supplier.

Frequently asked questions

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