Carpet Calculator
How much carpet to buy from a roll of fixed width: strips, length, seams, offcut waste and cost, for one room or several.
Result…
How it's calculated
Strips = width across the strips ÷ roll width, rounded up Length to buy = Σ strips × (run length + trim allowance) Carpet bought = length × roll width Seams = strips − 1 per room Offcut waste % = (bought − room area) ÷ bought × 100 Cost = area bought × price per m² (or yd²)
Works out how much carpet to buy for one or more rectangular rooms when the carpet comes off a roll of fixed width. Each room is covered with strips the full width of the roll, laid in whichever direction uses least carpet (or the direction you choose), with an allowance at the ends for trimming. Carpet is sold by the square metre in some countries and by the square yard in others; you pay for the full roll width, so the offcuts are part of the cost. Check the roll widths your supplier sells, since they vary by country and maker. For hard flooring sold in boxes, use the flooring calculator.
Your numbers, step by step
About the Carpet calculator
This carpet calculator works out how much carpet to buy when it comes off a roll of fixed width. Enter each room as length × width, the roll width your supplier sells and a trim allowance, and it lays whole strips the full width of the roll in whichever direction uses least carpet. You get the length to cut, the area you pay for, the number of strips and seams, the share that ends up as offcuts, and the cost if you add a price per square metre or square yard. Roll widths on sale vary by country and maker, so the width is always yours to enter. It works in metres or feet, and every step shows your own numbers, room by room. For laminate, vinyl or wood sold in boxes, use the flooring calculator instead.
How to use it
- Choose metric or imperial units.
- Under “Rooms, one per line: length × width”, type each room, for example 5 x 4, measuring into door frames and bays.
- Enter the “Roll width” your supplier sells and a “Trim allowance per strip” for cutting at the walls.
- Leave “Strips run” on “Least carpet”, or choose a direction if pile, light or seam position matters.
- Add a “Price per m²” or “Price per yd²” if you want the cost, then read the length to buy, seams and offcut waste.
Worked example
Two rooms of 5 × 4 m and 3.6 × 3 m, from a 4 m roll with 10 cm trim. The first room takes one strip of 5.1 m. The second takes one strip of 3.1 m laid across its width (one strip of 3.7 m the other way would waste more). Length to buy = 5.1 + 3.1 = 8.2 m, which is 8.2 × 4 = 32.8 m² of carpet for 30.8 m² of floor, so about 6.1% ends up as offcuts and there are no seams. At 25 per m², the carpet costs 32.8 × 25 = 820.
Updated
Questions people ask
How do I calculate how much carpet I need for a room?
Divide the room width by the roll width and round up to get the number of strips, then multiply the strips by the room length plus a trim allowance. That is the length to cut from the roll; multiply it by the roll width for the area you pay for.
Why do I pay for more carpet than my floor area?
Carpet is cut from a roll of fixed width, so a room narrower than the roll still takes the full width, and a room slightly wider needs a second strip. The extra becomes offcuts, which this calculator shows as the offcut waste percentage.
Which way should carpet strips run?
The least-carpet option picks the direction that needs the shortest length to buy. Fitters often prefer seams away from doorways and the pile running the same way in every strip, so you can fix the direction and compare the cost.
Is carpet priced per square metre or per square yard?
It depends on the country: many sell by the square metre, and the United States usually prices by the square yard. Choose metric for a price per m² or imperial for a price per yd², and the calculator converts the area you buy to match.
Can I use offcuts to cover part of the room?
Often, yes. A fitter may join an offcut to fill a narrow strip or an alcove, which can cut the length to buy. This calculator uses whole strips only, so treat its answer as an upper estimate and ask your fitter for the final cutting plan, especially for patterned carpet that must match.