Carpet calculator
Carpet calculator:
roll width, seams and cost
Carpet is cut from a roll 12 or 15 ft wide, so the waste is not a percentage you pick — it is whatever the roll width forces on your room. This works out the running feet, where the seams land, and how much the choice of roll actually costs you.
Enter measurementsThe decision nobody mentions
What the roll width costs you
Every stock width, one room. The showroom will quote you a price per square foot and let you assume the rest is arithmetic — but the width of the roll your carpet comes on decides how much of it you pay for and never walk on.
Run the calculator above and this table fills in with your own room.
Optional
What will it cost?
Every material the calculator worked out gets its own price. Each field starts at a typical US figure so you have something to work from — change any of them to what your own supplier charges.
These prices are approximate. They are national US retail figures, and what you actually pay varies with your region, your supplier, the season and how much you buy at once. Treat them as a starting point, not a quote — always price the job from your own supplier's current figures before you order.
Your prices
More in this series
The rest of the floor
A room is rarely one material and nothing else. The measurements you have entered here carry straight across to the floor next door, and to the pad under both.
- Flooring Calculator Laminate, vinyl plank, engineered wood and parquet
- Laminate Flooring Calculator Laminate planks, boxes, underlayment, transition strips and quarter round
- Vinyl Plank Flooring Calculator LVP planks, boxes, adhesive, underlayment and transition strips
- Hardwood Flooring Calculator Hardwood boards, cleats or staples, rosin paper and transition strips
- Underlay Calculator Flooring underlay rolls, strip layout and joint tape
- Carpet Pad Thickness and Density Thickness, density and what each one is actually for
Before the new goes down
What removing the old carpet costs
Pulling up carpet is cheap labor and expensive volume. The carpet and pad come up in minutes, but they are bulky enough to fill a skip long before they reach its weight limit — which is why haul-away, not the pulling, is what you are paying for.
Labor and haul-away
$0.50–$1.50
per square foot
Skip, if you do it yourself
$350
10 yard, about 2 tons
Tack strip
Reuse it
unless it is rusted or split
Tick the removal box in the calculator to fold this into your own figure.
Based on your result
What you'll need
Quantities update after every calculation. Carpet is quoted as what you buy off the roll, not what reaches the floor.
- Broadloom carpet
- Square feet off the roll, waste included
- Calculate above
- Carpet pad
- Square feet of floor, cut to fit
- —
- Tack strip
- Round the walls, less the doorways
- —
- Seam tape
- Only for the seams the roll width forces
- —
- Fitting kit
- Knee kicker, stretcher, tucker and seam iron
- 1 kit
The maths
How this carpet calculator works
Area times a waste percentage is the wrong model for carpet. The roll has a fixed width, so the room is covered in strips of that width — and whatever the last strip does not use is bought anyway. Turning the roll ninety degrees can remove a whole strip, so both directions are laid out and the cheaper one wins.
running feet = strips × run length
bought = running feet × roll width
seams = strips − 1
waste = (bought − floor) ÷ bought
The pad underneath is a separate order, cut to the floor rather than the roll. The underlay calculator sizes it by density and roll length.
- 01
Measure the room
One rectangle. Carpet is stretched in one piece per room, so an L-shaped space is two layouts, not one.
- 02
Pick the roll width
US broadloom comes 12 ft or 15 ft wide, and the mill decides which — the same pattern is rarely offered in both.
- 03
Lay the strips both ways
Running the roll along the length, then along the width. Whichever buys fewer square feet wins; on a tie, fewer seams wins.
- 04
Count the seams
One less than the number of strips, each running the full length of the strips it joins. A seam wants to run with the light and away from a doorway.
- 05
Work out what the roll forced
The gap between what reaches the floor and what came off the roll is the waste — and it is the roll width that set it, not your cutting.
- 06
Run the tack strip
Round the perimeter, stopping short at every doorway where a transition bar takes over.
Good to know
Carpet questions, answered
A 12 by 12 room is 144 sq ft of floor, but off a 12 ft roll you buy 12 running feet — 144 sq ft exactly, with no seam and nothing wasted. That is the rare case where the room and the roll agree. Make the room 13 ft wide and the same roll suddenly needs two strips and 312 sq ft.
It comes off a loom that is 12 or 15 ft wide, and it is not cut lengthways at the mill because a raw edge frays. So your room is covered by laying strips of the full roll width side by side, and whatever the last strip does not use is still on your invoice.
Made invisible, no. Made unobtrusive, yes. Run the seam in the same direction as the main light rather than across it, keep it out of doorways and traffic lines, and have the pile direction match on both sides. A seam across a hallway will show within a year however well it was made.
It is the strip that joins two pieces of carpet where the room is wider than the roll. The tape goes face-up under the joint, its heat-activated adhesive is melted with a seaming iron run along it, and both carpet edges are pressed down into the glue. Nothing is stitched — the seam holds because both pieces are bonded to the same strip underneath. It comes in 50, 66 and 100 ft rolls, and you only need it if the layout above gives you a seam at all.
Measure each step as its own piece: tread depth plus riser height, plus about 3 in for the nosing wrap. A standard flight of 13 steps takes roughly 20 running feet off a 12 ft roll. Stairs also want a firmer pad than the flat floor, which is a separate order.
Almost never — it is quoted separately and it is where a cheap job gets cheap. A thin, low-density pad lets the carpet flex at the backing and wear out years early. For a residential floor, look for 8 lb density at 7/16 in thick, and use the underlay calculator to size it.
Whichever wastes less on your room, and the table above works that out. As a rule, rooms up to 12 ft wide suit the 12 ft roll, and rooms between 12 and 15 ft strongly favour the 15 ft roll — a 14 ft room off a 12 ft roll needs a second strip for two feet of coverage.
Usually not. It is nailed down around the perimeter and it survives a carpet change fine unless it has rusted, split or pulled loose. Replace it in bathrooms and anywhere it has got wet, and add new where a doorway or a wall has moved.