Carpet Calculator: How Much Carpet to Buy
Carpet comes off a roll of fixed width, so the room area is not what you pay for. We plan the cut both ways and show the one that wastes less.
Your estimate
Buy 36 sq yd
of carpet from a 12 ft roll
- Room area
- 21.7 sq yd
- Cut
- 2 × 13.5 ft from a 12 ft roll1 seam
- Offcut
- 66%
- Carpet pad
- 22.7 sq yd
- Tack strip
- 53 ft · 14 × 4 ft
Add a price per square yard to see the cost.
How we got this: 2 pieces across the room × (13 ft + 6 in trim) × 12 ft roll width = 36 sq yd.
This layout has 1 seam. Keep seams out of doorways and main walkways, and lay every piece with the pile in the same direction.
Ask the store to quote the cut length from the roll, not just the room area: carpet is sold by the length cut off the roll.
How the calculation works
- Strips. We divide the room width by the roll width to get the number of pieces, each as long as the room plus a few inches to trim at each wall.
- Both directions. We repeat this with the pieces running the other way and keep the layout that needs less carpet.
- Pad and tack strip. Pad covers the room area plus 5%. Tack strip (gripper rod) runs around the walls, except across doorways.
Imperial example: a 13 × 15 ft room from a 12 ft roll needs two pieces 13 ft 6 in long: 36 sq yd with one seam. From a 15 ft roll it is one piece: 22.5 sq yd, no seam.
Metric example: a 4 × 5 m room from a 4 m roll is one piece 5.15 m long: 20.6 m², no seam.
Guides to save and share
Chart as a table: How much carpet do I need?
| Room | 12 ft roll | 15 ft roll |
|---|---|---|
| 10 × 10 ft (bedroom) | 14 sq yd | 17.5 sq yd |
| 10 × 12 ft (kitchen) | 14 sq yd | 17.5 sq yd |
| 12 × 15 ft (living room) | 20.7 sq yd | 20.8 sq yd |
| 15 × 20 ft (open plan) | 41.3 sq yd | 34.2 sq yd |
| 20 × 25 ft (basement) | 68 sq yd | 68.3 sq yd |
How much carpet waste is normal?
| Room | Typical offcut | Why |
|---|---|---|
| Narrower than the roll | 5–20% | One piece, trimmed on one side. |
| Slightly wider than the roll | 40–70% | A second full-width strip for a narrow gap; consider the wider roll. |
| L-shaped or with closets | 15–30% | Extra pieces and seams for the alcoves. |
Common mistakes
- Buying by room area. You pay for the full width of every piece cut from the roll.
- Running pieces in different directions. Pile reflects light differently, so seams show.
- Putting a seam across a doorway or the main walkway, where it wears first.
- Forgetting the pad in the budget. It is usually priced separately per square yard.
What else you'll need
- Carpet pad (underlay) and pad tape or staples.
- Tack strip (gripper rods) and seaming tape for any seams.
- Door bars or transition strips at doorways.
- A knee kicker and power stretcher (often rented), a carpet knife and a stair tool.
Frequently asked questions
How much carpet do I need for a 12 × 12 room?
From a 12 ft roll, one piece 12 ft 6 in long: about 16.7 sq yd. A 12 × 13 ft room would need a second strip or a 15 ft roll.
How do I convert square feet to square yards?
Divide by 9. 225 sq ft is 25 sq yd.
What roll widths does carpet come in?
In the US, mostly 12 ft and 15 ft. In the UK, Ireland and Australia, 4 m and 5 m, with some 3.66 m.
Do I need carpet pad?
Yes, unless the carpet has a built-in backing that says otherwise. Pad makes carpet last longer and feel better underfoot.
How much extra carpet should I order?
It depends on the layout, not a fixed percentage. Plan the cut from the roll width; add a few inches at each wall for trimming.
Related calculators
This is an estimate. Actual use depends on the material, the surface, the installation method, waste and site conditions. Check quantities with your supplier before you buy.