Enter your room sizes and the roll width you are buying - 3.66 m (12 ft) - pick a wastage allowance, and get the linear metres of broadloom to order, the floor area in square metres, and how many seams the layout needs.
Floor area
20.00 m²
Carpet bought
32.21 m²
Seams
1
Run by room
Floor area 20.00 m² (20.00 m²). Carpet is sold by the running length of the roll, so the offcut of a part-used strip is paid for too.
Broadloom carpet is the odd one out among floor coverings: it comes off the roll at a fixed width and you buy it by the running length, not by loose square metreage. So the real question is not the room’s area - it is “how many linear metres of this roll width do I need once the strips are laid and seamed”. For each room the calculator lays strips the roll-width wide and works out the run:
strips (along length) = ceil( room width ÷ roll width ) → run = strips × room length
strips (along width) = ceil( room length ÷ roll width ) → run = strips × room width
linear run = the shorter of the two (Auto), summed across rooms
to buy = linear run × wastage
carpet area = run to buy × roll width
A room no wider than the roll drops in as a single seam-free piece. A wider room needs a second strip and a seam, and the leftover of that strip is carpet you still pay for - the price of a fixed roll width. The runs are summed per room because pile direction and seam visibility mean offcuts do not carry between rooms the way plank flooring does.
Stairs are the special case. A flight is carpeted with one continuous runner that wraps each step, so the carpet length is the number of steps times the tread plus the riser, and it always runs down the flight in one piece - you cannot seam across the steps. Add a staircase in the calculator and it works the runner out and pools it with your rooms. For more on each part of the job, see how much carpet do I need, how to measure stairs for carpet, and how much carpet costs.
This example follows the unit system you pick in the calculator above.
A 5 m × 4 m living room on a 3.66 m (12 ft) broadloom roll, 10% wastage:
The roll width decides how many strips - and seams - a room needs, so it matters more than any other input. These are the widths you are likely to be offered:
| Region | Standard roll widths | Sold by |
|---|---|---|
| US / Canada | 12 ft (3.66 m); also 15 ft, occasionally 13.5 ft | Square yard (or square foot) |
| UK | 4 m and 5 m; 3 m on some ranges | Square metre |
| Australia | 3.66 m and 4 m | Broadloom metre |
| New Zealand | 3.66 m | Broadloom (lineal) metre |
A broadloom metre is a 1 m length cut from the full roll width - 3.66 m² of carpet from a 3.66 m roll - and is usually the smallest amount you can buy. For the full picture see standard carpet roll widths and how carpet is sold.
In Canada, broadloom carpet comes in 12 ft (3.66 m) rolls, with 15 ft and occasionally 13.5 ft also made, and it is sold by the square yard (and increasingly the square foot). However it is priced, the roll arrives at a fixed width, so the figure that really matters is the running length you need at that width - a 12 ft roll yields four square yards for every linear foot you take off the bolt, so the running length is what drives the price. Set the roll width in the calculator above to match what your retailer stocks so the run is right.
For the recognised installation detail - subfloor prep, underlay, seam placement and stretching - see the CRI 105 standard for residential carpet installation.
A 4 m × 5 m room is 20 square metres. On a 4 m wide roll it drops in as a single seam-free piece, so you need 5 linear metres of broadloom, plus a little for wastage. Because the room is no wider than the roll there is no offcut along its length. Enter your exact room and roll width above for any size.
Broadloom carpet is made in fixed roll widths. In the UK rolls are 4 m and 5 m; in Australia and New Zealand they are 3.66 m and 4 m. In the US and Canada the standard is 12 ft (3.66 m), with 15 ft also made. Pick the width your retailer stocks in the calculator, because it decides how many strips - and seams - a wide room needs.
It is sold by the running length of the roll, not by loose area. UK carpet is priced by the square metre; Australian and New Zealand carpet by the broadloom metre, which is a 1 m length of the full roll width; US and Canadian carpet by the square yard. However it is priced, the roll comes in a fixed width, so the linear run you need at that width is what drives the cost.
Because carpet comes off the roll at a fixed width. If your room is narrower than the roll you still buy the full width and trim the surplus; if it is wider you need a second strip and seam the two together, and the second strip is rarely used to the inch. That trimmed surplus is the price of a fixed roll width, which is why this calculator works in linear run and roll width rather than loose square metreage.
Run the strips so the pile (nap) leans the same way across the whole floor and seams fall away from doorways and high-traffic lines where they show and wear. The calculator's "Auto" setting picks the strip direction that needs the shortest run and the fewest seams; switch it to "along the length" or "along the width" if you want to force the lay to suit the light or the traffic.
Allow about 5% for plain carpet in simple square rooms, 10% as a standard allowance, and 15% for patterned carpet where the pattern has to repeat across seams or the pile direction forces extra trimming. Stairs, bay windows and irregular rooms also push the figure up. It is safer to round up than to be a strip short, because a later batch can vary slightly in colour.
Measure each room separately. Unlike planks, carpet offcuts do not carry cleanly from one room to the next - the pile direction has to stay consistent and a small offcut would show as a seam - so the calculator works out the linear run for each room on its own and adds them up. Enter every room you are carpeting in the same material and it pools the run for you.
A flight is carpeted with one continuous runner that wraps every step, so the carpet length is the number of steps times the tread (going) plus the riser. A 13-step flight with a 250 mm tread and a 200 mm riser needs 13 × 0.45 = about 5.85 m of runner. Add a staircase in the calculator - enter the steps, tread, riser and stair width - and it works the run out and adds it to your rooms. See our guide on how to measure stairs for carpet for the method.
Carpet itself runs from budget to premium per square metre or broadloom metre, and fitting, underlay, gripper and door bars are usually charged on top - often a third to half of the installed price. Because rates swing so much by region and quality, the honest way to budget is to get the carpet quantity first, then price each line locally. This calculator gives you the broadloom to buy; our guide on how much carpet costs breaks the rest down.
Not directly - this is a broadloom calculator, and carpet tiles are a different product sold by the box like floor tiles. For modular carpet tiles, take your floor area, divide by the area one tile covers, add about 5-10% for cuts, and round up to whole boxes - the same method as the tile and flooring calculators. Broadloom is the one that needs the roll-width math this tool handles.
Turn your room sizes into the linear yards of broadloom to order, with a 12x12 example.
Read guide→Estimate carpet cost from the quantity - carpet, underlay, gripper, fitting and uplift.
Read guide→Count the steps, measure the tread and riser, and turn it into a runner length.
Read guide→Standard broadloom roll widths by country, and why the width decides your seams.
Read guide→Square yards, square feet, square metres and broadloom metres explained, with conversions.
Read guide→Planks and boxes of laminate, vinyl or hardwood flooring, with layout wastage.
Open calculator→How many tiles, boxes, adhesive and grout to buy for a floor or wall, with wastage and cost built in.
Open calculator→How many rolls of wallpaper to buy for a room, with the pattern repeat built in.
Open calculator→Litres of paint for walls and ceilings, with coats and coverage built in.
Open calculator→Total area of any room or lot in sq ft, m², sq yd and acres.
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