Guide · Calculator

Carpet calculator: how much carpet do I need?

Carpet is measured in square metres but bought in lineal metres off a roll of fixed width. Enter the rooms and the roll width and the calculator cuts each room along the roll the way a carpet estimator does: drops, lineal metres, seams and the square metres you actually pay for. The method is explained below it, with a worked example.

Carpet calculator

Units Metres and m²Feet and sq ft Roll width 3.66 m4.0 m5.0 mCustom Trim allowance per drop (m) Pattern repeat (m, optional) Waste % on lineal metres Rate (optional) Rate is per m² boughtlineal metre

Rooms (length × width in metres)

Add a room

Room	Net	Drops run	Drops × length	Lineal	Bought	Seams
Turn on JavaScript to use the calculator. The worked example below shows the same steps by hand.

Example figures are filled in. Waste starts at 0% because the offcut is already inside the lineal metres; many estimators add 5% to 10% for patterned carpet or as a margin for offcuts that cannot be reused. Each room is cut on its own. Nothing you type leaves this page.

How the calculator works

Every piece cut off a roll is a drop, and the supplier charges for the full roll width along every metre cut. So the question is not how big the room is, but how many drops it needs and how long each one is. For each room the calculator:

1. Decides which way the drops run: along the room's length, or across it. On "Best" it tries both and takes the one with fewer lineal metres (if they tie, the one with fewer seams).
2. Divides the side across the roll by the roll width and rounds up. That is the number of drops.
3. Takes the side along the roll and adds the trim allowance. That is the drop length. If you enter a pattern repeat, the drop length is rounded up to a whole number of repeats.
4. Multiplies drops by drop length to get the lineal metres. Seams are drops minus one.

It then totals the rooms, applies any waste percentage to the lineal metres, and multiplies by the roll width to get the square metres bought. Comparing that with the net floor area shows how much of the order ends up as offcut. A rate can be per square metre bought or per lineal metre, to match your price book.

A worked example

A three bedroom home has carpet in the bedrooms, the walk-in robe, the hall and a separate lounge. Lengths are the first figure and widths the second. The hall is set to run along its length; every other room is on "Best".

The order is 26.0 lineal metres, which is 26.0 × 3.66 = 95.16 m² of carpet for 64.98 m² of floor. That is 46.4% more carpet than floor, almost all of it in three rooms: the hall (a 1.1 m wide room on a 3.66 m roll), the walk-in robe, and the lounge, which is wider than the roll in both directions and needs a second drop. There is one seam, in the lounge. At $55 per m² bought, the carpet line is $5,233.80.

How the direction changes the lineal metres

Here is every room cut both ways on the same roll:

Running every room along its length would need 29.4 lineal metres (107.60 m², $5,918.00), which is $684.20 more than the example for exactly the same floor. Bed 1 is the room where getting it wrong hurts most: 3.9 m across the roll needs two drops, so the wrong direction nearly doubles its carpet.

The hall shows the other side of the decision. On "Best" the calculator would cut it across: two short drops of 1.2 m, saving 3.1 lineal metres (11.35 m², $624.25). But that puts a seam across the hall, where everyone walks, and turns the pile sideways to the rooms either side. Most estimators would pay for the long drop, or plan to cut the hall from another room's offcut. That is why the direction can be set per room.

Why square metres alone under-order carpet

A quote built from net floor area plus a flat 10% would order 64.98 × 1.10 = 71.48 m² for this house. The roll needs 95.16 m². The gap, 23.68 m², is $1,302.40 at the example rate, and it comes out of the contractor's margin, not the builder's. Carpet waste is not a percentage of the floor. It is the strip beside each drop when a room is narrower than the roll, plus whole extra drops when it is wider, and a percentage cannot see either. Waste for hard floors works differently, and the flooring waste percentage guide covers that.

Roll widths by country

• Australia and New Zealand: 3.66 m (12 feet) is the most common width, with some ranges in 4 m. Lineal metres times roll width gives the square metres bought.
• UK and Ireland: 4 m and 5 m rolls are common, and carpet is usually priced per square metre. The drop method is the same.
• US and Canada: carpet usually comes in 12 ft or 15 ft rolls, with some ranges in 13 ft 2 in (about 4 m), and is priced by the square yard (9 sq ft). Switch the calculator to feet and it adds a square yard figure.

A wider roll is not automatically cheaper. On a 5 m roll the example lounge fits in one drop with no seam, but every other room already fitted on 3.66 m, so the whole house needs 22.6 lineal metres and 113.00 m² bought, more carpet than on the narrower roll. Check which widths the selected range actually comes in before choosing. The carpet lineal metres and roll width guide works through 3.66 m, 4 m and 5 m on the same rooms.

Pile direction and seams

Carpet pile leans one way, and light catches it differently from each side. Drops in the same room should run the same way, and ideally the pile continues through a doorway into the next room, so the colour reads as one floor. Seams belong out of main walkways and away from strong light across a large window, where a join shows. Those rules sometimes cost lineal metres. The calculator gives the numbers for each choice; the estimator decides.

Trim allowance and pattern repeat

Walls are rarely straight and square, so each drop is cut a little long and trimmed in place. A 0.1 m allowance per drop, about 50 mm at each end, is a common starting point; use more for out of square rooms or long drops.

Patterned carpet has to line up across every seam, so each drop must start at the same point in the pattern. Enter the pattern repeat (it is printed on the sample or the specification sheet) and each drop is rounded up to a whole number of repeats. With a 0.6 m repeat, Bed 1's 4.0 m drop becomes seven repeats, 4.2 m. The calculator only adjusts the length; side matching, and the extra a supplier may ask you to allow on a large patterned job, still need checking with the range's specification.

Stairs

Stairs are not in the calculator. Each step is cut as its own piece, or the staircase is cut as a runner, and most contractors price carpet on stairs per step or per staircase rather than by area. Measure each step's tread, riser and nosing as you would for any floor on a stair; the guide to measuring stairs shows how. A landing can go in the calculator as a room.

What the calculator does not do

It cuts every room on its own, which is a safe, conservative order. Real carpet estimators often do better across a whole house: the strip left beside the lounge's second drop can become a robe, and a cut can be planned so a seam falls under a bed rather than in a doorway. The calculator does not reuse offcuts between rooms, plan seams around traffic and light, or handle L-shaped rooms (split those into rectangles and check where the seam falls). It also leaves out naplocks, underlay if it is not in your rate, removal of old carpet and floor preparation. Price those as their own lines.

How Squaro does this

Squaro reads which rooms are carpet from the selections and measures each one from the printed dimension strings on the plan, showing the page and dimension text it used. It cuts each room along the roll at the roll width you set, in the direction that uses fewer lineal metres, and prices the area bought at your rate, with naplocks, staircases and scrape up from your rules. You can change the lineal metres on any room when you plan offcuts or seams differently, and you check every line before the quote goes out. See carpet quoting software for the rules you can set, or the guide to quoting from builder plans for the whole method.

Related reading

• Carpet lineal metres and roll width, explainedWorking out carpet off a 3.66 m or 4 m roll, choosing the cut direction, and pricing what you buy.
• Flooring waste percentage, and when to round up to packsChoosing a waste figure, applying it in the right order, and rounding to whole packs.
• How to quote flooring from builder plansThe full method, from the builder's pack to a priced quote, with a worked hybrid example.

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