Carpet is sold off a roll 12 or 15 ft wide, so you pay for whole strips, not for your floor area. A 16 × 14 ft living room and a 12 × 11 ft bedroom have 356 sq ft (39.6 sq yd) of floor, but cut from a 12 ft roll they take 41 ft 6 in of roll, which is 55.3 sq yd to buy. On a 15 ft roll the same rooms take 28 ft, 46.7 sq yd, with no seam at all.
How the carpet calculator works
Each room gets 3 in extra on every wall, the trimming allowance in the Carpet and Rug Institute's installation standard (CRI 105, section 5.3). The trimmed room is then cut into strips that run along the roll: as many full-width strips as fit, plus one fill strip for the rest. Every piece keeps the same pile direction, which CRI 105 requires for adjoining pieces of the same carpet. Fill strips and stair pieces are first fitted into offcuts left by earlier rooms, and only then cut from new roll.
strips = (room width + 6 in) ÷ roll width, rounded up; each strip is (room length + 6 in) long
square yards to buy = linear feet of roll × roll width in ft ÷ 9
With "Fewest seams" the calculator tries each room both ways round and keeps the direction with fewer seams, then the one that uses less roll.
Worked example: living room and bedroom on a 12 ft roll
- Living room 16 × 14 ft, trimmed to 16 ft 6 in × 14 ft 6 in. Run along the length, the 14 ft 6 in width needs a 12 ft strip and a 2 ft 6 in strip, each 16 ft 6 in long: 33 ft of roll. Run across, the 16 ft 6 in needs a 12 ft strip and a 4 ft 6 in strip, each 14 ft 6 in long: 29 ft. Both have one seam, so the shorter wins: 29 ft, one 14 ft seam.
- Bedroom 12 × 11 ft, trimmed to 12 ft 6 in × 11 ft 6 in. The 11 ft 6 in fits the 12 ft roll, so it is one piece 12 ft 6 in long.
- Roll: 29 + 12.5 = 41 ft 6 in, × 12 ft = 498 sq ft = 55.3 sq yd.
- Left over: a 7 ft 6 in × 14 ft 6 in offcut beside the living room fill strip, plus the trim.
- Pad: 356 sq ft + 10% = 391.6 sq ft, 44 sq yd. Tack strip: 106 ft of walls minus two 36 in doorways is 100 ft, + 10% = 28 pieces of 4 ft.
Add 13 stairs 36 in wide with 10 in treads, 7½ in risers and 2 in for the nose, and each step needs a piece 3 ft × 19½ in. All 13 come out of the living room offcut, so the roll stays at 41 ft 6 in. The pad rises to 52 sq yd and the tack strip to 39 pieces, one strip per tread.
Roll widths: 12 ft, 13 ft 6 in or 15 ft
| Rooms in the example | Roll | Linear length | To buy | Seams |
|---|---|---|---|---|
| 16 × 14 ft + 12 × 11 ft | 12 ft | 41 ft 6 in | 55.3 sq yd | 1 (14 ft) |
| 16 × 14 ft + 12 × 11 ft | 15 ft | 28 ft | 46.7 sq yd | none |
Most broadloom carpet is made 12 ft wide, many lines also 15 ft (Shaw lists both), and some 13 ft 6 in. A room just over 12 ft wide is where a wider roll pays off.
Where the seams go
CRI 105 asks installers to keep seams to a minimum and, where possible, to run them the length of the room, parallel to the main traffic, away from pivot points such as the bottom of the stairs, not across a doorway and not where window light rakes across them. The room list under the drawing tells you which way each room's roll runs and how long its seams are, so you can check that the seam lands where it will not be seen.
Carpet for stairs
Measure one step as tread plus riser plus an inch or two to wrap the nose, then multiply by the number of steps. CRI 105 recommends running the carpet's length up the stairs, with the pile running down, which is how the calculator cuts the pieces. A 36 in stair from a 12 ft roll gives four pieces side by side, so offcuts often cover a whole flight. For a new staircase, the stair calculator works out the treads and risers first.
Pad and tack strip
Pad is laid butted, not overlapped, over the floor and the stairs, and is sold by the square yard. Tack strip runs along every wall except across doorways, with a gap "slightly less than the thickness of the carpet but not exceed 3/8 inch" (CRI 105), plus one strip on each tread.
What to do next
- Hard floors in the other rooms? The flooring calculator counts cartons for vinyl plank, laminate and hardwood.
- The installed price, with removal of the old carpet, is in the flooring cost calculator.
- New shoe molding or baseboard where carpet meets a hard floor: the baseboard calculator.
- Odd-shaped room? Split it into rectangles with the room square footage calculator and add each part as a room.
All floor tools are on the floors, tile and trim page.