Carpet Calculator
Square feet, square yards and linear metres of carpet for a room or L-shaped room, allowing for roll width, seam placement and waste — with cost per yd², ft² or m².
Carpet Calculator: with the default inputs, carpet to buy is 198 ft².
For an L-shape, split the floor into two rectangles and enter the second under More options.
US broadloom is almost always 12 ft. 13 ft 2 in (4 m) and 15 ft are available but special-order.
Trimming, pattern match and a piece kept for repairs. 5% for a plain cut pile, 15–20% for a patterned carpet.
Linear run off the roll × roll width, including waste. This is what you pay for.
- Floor area
- 180 ft²The actual floor being covered.
- Length off the roll
- 16.5 ftSwitch to yards or metres — carpet is cut to a length, not an area.
- Widths of carpet
- 1How many full roll widths the layout needs.
- Seams
- 0
- Waste against floor area
- 10%How much more carpet you buy than floor you cover.
- How to run it
- Run the carpet along the 15 ft direction: 1 width of 12 ft carpet, 15 ft off the roll.
- Carpet cost
- $0.00
- Pad cost
- $0.00
Assumptions
- Broadloom carpet comes off a fixed-width roll; pieces are not rotated, because pile direction must stay consistent.
- Each rectangle is laid with strips running whichever way needs the shorter run off the roll.
- Waste covers trimming, squaring and a repair piece; patterned carpet needs more because seams must match the repeat.
| Roll width | Widths needed | Length off the roll (ft) | Carpet to buy (ft²) |
|---|---|---|---|
| 12 ft | 1 | 16.5 | 198 |
| 13 ft 2 in (4 m) | 1 | 16.5 | 217 |
| 15 ft | 1 | 13.2 | 198 |
Same room, same waste allowance — only the roll width changes.
How this is worked out
The formula
For each rectangle, try both directions and keep the cheaper one: widths = ⌈across ÷ roll width⌉ run = widths × along Length off the roll = Σ run × (1 + waste) Carpet to buy = length off the roll × roll width Seams = Σ (widths − 1), plus one where an L-shape is joined
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Room shape
- For an L-shape, split the floor into two rectangles and enter the second under More options.Rectangle · L-shape (two rectangles, More options)
- Room length
- A number.in ft, in, yd, m, cm · 0 or more · defaults to 15
- Room width
- A number.in ft, in, yd, m, cm · 0 or more · defaults to 12
- Carpet roll width
- US broadloom is almost always 12 ft. 13 ft 2 in (4 m) and 15 ft are available but special-order.in ft, m, in, cm · 1 or more · defaults to 12
- Waste allowance
- Trimming, pattern match and a piece kept for repairs. 5% for a plain cut pile, 15–20% for a patterned carpet.a percentage · from 0 to 100 · defaults to 10
- Second rectangle length(under More options)
- A number.in ft, in, yd, m, cm · 0 or more · defaults to 8
- Second rectangle width(under More options)
- A number.in ft, in, yd, m, cm · 0 or more · defaults to 6
- Carpet price(under More options)
- Leave 0 to skip the cost estimate. Carpet is usually priced per square yard in the US.in dollars · 0 or more · defaults to 0
- Price is per(under More options)
- Choose one of 3 options.Square yard · Square foot · Square metre
- Pad price per yd²(under More options)
- Pad is cut to the floor area, not the roll width, so it wastes far less.in dollars · 0 or more · defaults to 0
What you get back
- Carpet to buymain answer
- Linear run off the roll × roll width, including waste. This is what you pay for.
- Floor area
- The actual floor being covered.
- Length off the roll
- Switch to yards or metres — carpet is cut to a length, not an area.
- Widths of carpet
- How many full roll widths the layout needs.
- Seams
- Waste against floor area
- How much more carpet you buy than floor you cover.
- How to run it
- Carpet cost
- Pad cost
What this assumes
- Broadloom carpet comes off a fixed-width roll; pieces are not rotated, because pile direction must stay consistent.
- Each rectangle is laid with strips running whichever way needs the shorter run off the roll.
- Waste covers trimming, squaring and a repair piece; patterned carpet needs more because seams must match the repeat.
About this calculator
Carpet is sold off a roll of fixed width — 12 ft almost everywhere in the US — and cut to a length. That single fact is why a 14 × 20 ft room can cost you 40% more carpet than its floor area, and why the direction you run it matters more than the waste percentage.
How to use it
Enter the room's length and width and leave the roll at 12 ft unless your dealer has told you otherwise. The calculator tries the carpet running both ways and reports the cheaper layout under How to run it — that alone often saves a hundred square feet.
For an L-shaped room, switch the shape to L-shape and split the floor into two rectangles under More options. The calculator lays each one separately and adds a seam where they join.
Why roll width matters
If the room is narrower than the roll, you get one clean piece with no seam and waste only from trimming. The moment a dimension exceeds 12 ft in both directions, you need a second width, and the offcut from that second width is usually scrap — you can't rotate it, because cut pile has a nap and a rotated piece will read as a different colour under the same light.
Take a 14 × 20 ft room. Run the carpet along the 20 ft direction and you need two 20-ft widths, 480 ft² for a 280 ft² floor. Run it along the 14 ft direction and two 14-ft widths is 336 ft². Same room, 144 ft² of difference.
Seams
Every extra width is a seam. Good seam practice, in rough order of importance:
- Run seams into the main light source, not across it — a seam lit from the side casts a shadow line.
- Never put a seam in a doorway or across a main traffic path; that's where it will open first.
- Keep the pile direction consistent across every piece. Mark the arrows on the back before you cut.
- Seams in a bedroom under furniture are free. Seams in the middle of a living room are forever.
Reading the results
Carpet to buy is the linear run times the roll width, including waste — the number your dealer will quote from. Waste against floor area is the honest cost of the roll width. Above about 20%, ask whether a 13 ft 2 in (4 m) roll changes the picture; the table under the results does that comparison for your room. Pad is cut to the floor shape, so it wastes far less, which is why it's costed separately.
Frequently asked questions
▸How much carpet do I need for a 12 × 15 room?
Twelve feet matches the roll width exactly, so you buy a single 15-ft length: 180 ft² of floor, 198 ft² with 10% waste, and no seam. That's the ideal case.
▸Why is carpet sold in square yards?
Historically because broadloom came off 12-ft rolls and a running yard of it is exactly 4 square yards. A square yard is 9 square feet, so divide square feet by 9 to compare a per-yard price with a per-foot one.
▸How much waste should I allow for carpet?
5% for a plain cut pile in a simple rectangle, 10% for a normal room with doorways and closets, and 15–20% for a patterned carpet, where every seam has to match the repeat.
▸Can I turn an offcut sideways to avoid a seam?
No. Cut pile has a nap, and a piece rotated 90 or 180 degrees reflects light differently — it will look like a different shade of the same carpet. Keep every piece running the same way.
▸Does the pad cost the same as the carpet?
No — pad is cut to the floor shape rather than off a fixed-width roll, so it wastes almost nothing and is priced separately. Budget a few dollars a square yard, and don't cheap out: the pad does most of the work in how the carpet wears.
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