How much carpet do you need? Add your rooms and pick the roll width. It works out the drops both ways, then shows the metres to order, the m² you'll pay for, the waste and the seams, with the working.
Measure the length and width at the widest points. Walls bow and corners are rarely square, so measure in more than one place and use the biggest figure. Cormar's advice is to measure at the longest and widest points even when a room has chimney breasts, recesses or a bay window.
Measure into the middle of each doorway, not just to the door, and into bays, alcoves and door reveals. Enter sizes in metres: 4.25 is 4 m 25 cm, or type 425cm. Don't add your own allowance, because the calculator already adds the trim to every drop.
Broadloom carpet comes in fixed roll widths, and in the UK those are usually 4 m and 5 m. Cormar makes all its loop and twist pile carpets in both "to avoid seams in wider rooms", but not every range comes in both, so check the product first.
You buy drops cut off the roll, and every drop is the full roll width whether the room needs it or not. A room 3.6 m across wastes a 0.4 m strip on a 4 m roll and a 1.4 m strip on a 5 m roll. A room over 4 m in both directions needs a seam on a 4 m roll, but a 5 m roll may cover it in one piece.
Wider isn't automatically better: a 5.5 × 3.0 m room buys 22.40 m² off a 4 m roll but 28.00 m² off a 5 m roll. Cormar also recommends planning a job from one width, as colour matching between 4 m and 5 m widths, or carpet bought at different times, can't be guaranteed.
Carpet laid with its pile running the other way can look like a different shade. The US installation standard CRI 105 requires adjacent pieces of the same carpet to have the pile running the same way, and Gerflor's Gradus guidelines have multi-width fits cut as consecutive pieces from the roll, pile the same way. In the UK, BS 5325 is the code of practice for installing textile floor coverings.
So the calculator never turns a drop to save carpet. It picks the direction that buys least and shows the other, for when the pile has to run a set way: CRI 105 names the pile lying towards the entrance as ideal, where other factors allow.
Where a room is wider than the roll, the widths are joined with a seam. Seams can show, so plan where they go. The general practice set out in CRI 105 is to:
Some carpets need their factory edges trimmed before seaming, so don't plan to the last centimetre of roll width. This calculator counts seams; it doesn't place them.
A patterned carpet repeats its design at a set distance, the pattern repeat, shown on its specification. For the pattern to line up at a seam, neighbouring drops must start at the same point in the design, so each drop is cut to whole repeats: with a 0.64 m repeat, a 4.30 m drop becomes 4.48 m.
That's the minimum. Brintons expects patterns kept matched and aligned in both length and width, and CRI 105 calls for enough material to match. Centring a design, carrying it through a doorway or matching long runs can take more, so check the fitting instructions and your supplier before ordering.
All use the default 0.10 m trim per drop. Enter any of them above to see the full working.
| Room | Roll | Layout | Order | Bought | Waste | Seams |
|---|---|---|---|---|---|---|
| 3.60 × 4.20 m | 4 m | 1 width × 4.30 m, drops along the 4.20 m side | 4.30 m | 17.20 m² | 2.08 m² (12.1%) | 0 |
| Same room, turned | 4 m | 2 widths × 3.70 m, drops along the 3.60 m side | 7.40 m | 29.60 m² | 14.48 m² (48.9%) | 1 |
| 5.50 × 3.00 m | 4 m | 1 width × 5.60 m, drops along the 5.50 m side | 5.60 m | 22.40 m² | 5.90 m² (26.3%) | 0 |
| 5.50 × 3.00 m | 5 m | 1 width × 5.60 m, drops along the 5.50 m side | 5.60 m | 28.00 m² | 11.50 m² (41.1%) | 0 |
| 4.00 × 4.00 m | 4 m | 1 width × 4.10 m either way, but nothing spare to trim at the side walls | 4.10 m | 16.40 m² | 0.40 m² (2.4%) | 0 |
| 3.60 × 4.20 m, 0.64 m repeat | 4 m | 1 width × 4.48 m (7 repeats), drops along the 4.20 m side | 4.48 m | 17.92 m² | 2.80 m² (15.6%) | 0 |
Real jobs have offcuts worth reusing, stairs and seams to plan. A proper cutting plan nests every drop on the roll and often saves material: that's what BillyBot's cutting plan software does. Once you know what to order, see how to quote a flooring job. Fitting LVT or laminate? Use the flooring pack calculator, and the smoothing compound calculator for the floor prep.
Work it out drop by drop rather than adding a percentage. Each drop is the room length plus a trimming allowance, cut at the full roll width, so the waste depends on how the room fits the roll. Fitting guides ask for carpet cut oversize for trimming in; one UK manufacturer's guide says approximately 50 mm. This calculator adds 0.10 m to every drop by default, which you can change.
Use the width that buys the least carpet with seams you can accept, as long as the carpet is made in that width. A room over 4 m in both directions needs a seam on a 4 m roll but may go down in one piece off a 5 m roll, while a narrow room on a 5 m roll pays for a wide strip of waste. The calculator compares both widths for your rooms.
Yes. When a room is wider than the roll, widths are joined with a seam, commonly with hot-melt seaming tape or by sewing, depending on the carpet, and cut edges are sealed so tufts don't work loose. Good practice is to keep seams to a minimum, run them the length of the room, and keep them out of doorways, busy walkways and places where light falls across them.
Stairs need a different method from rooms. Each step is measured as its tread and riser, including the nosing, and winders and landings are measured on their own, so a room calculator will get the quantity wrong. BillyBot's cutting plan software works out treads, risers, winders and landings, including the gripper.
Enter the repeat from the carpet's specification and each drop is rounded up to a whole number of repeats, so neighbouring drops can be matched. That's the minimum: centring a design, or matching through doorways and over long runs, can take more, so check the fitting instructions and ask your supplier.
You order a length off the roll, but carpet is often priced per square metre, so you pay for the length times the roll width, not the floor area. A 4.30 m drop off a 4 m roll is 17.20 m² bought, even when the room is 15.12 m². Add a price per m² and the calculator costs the carpet you actually buy.
BillyBot works out the cutting plan for the whole job, rooms and stairs together, so you order the right material with less waste. Then it prices the material into a quote on your own rates, ready for you to check and send.
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