How much carpet do I need?
Carpet is not bought by floor area. It is cut off a roll of fixed width — almost always 12 feet — so you buy full-width strips long enough to cover the room, and everything left over is waste.
An 18 × 12 ft room is the ideal case: one 18 ft strip off a 12 ft roll covers it exactly. 216 square feet of floor, 216 square feet bought, zero waste. That is 24 square yards.
An 18 × 13 ft room is 234 square feet of floor and needs two strips — 36 feet of roll, which is 432 square feet bought. One extra foot of room width takes waste from 0% to 85%. This is the single most important thing to understand before you price carpet, and it is why installers ask the room dimensions rather than the area.
How the calculation works
Strips = room width ÷ roll width, rounded up. Roll length needed = room length × strips. Square feet bought = roll length × roll width, and square yards = that ÷ 9.
The roll runs along the longer dimension so any seam runs the short way and there are fewer of them. An installer may lay it the other way if the pile direction or a doorway demands it, which changes the quantity — worth asking before ordering.
Carpet is quoted per square yard almost everywhere in North America, and there are 9 square feet in a square yard. Comparing a per-square-yard price with a per-square-foot price without converting makes carpet look three times cheaper than it is.
Padding is different: it comes in rolls that simply butt together, so you buy actual floor area with only a small trim allowance. Never reuse old padding under new carpet — it is compressed where the traffic was and the new carpet will wear in exactly the same lines.
Typical carpet cost, mid-2026
| Material | Unit | Typical range |
|---|---|---|
| Builder-grade carpet | per sq yd | $12.00 – $25.00 |
| Mid-range residential | per sq yd | $25.00 – $45.00 |
| Wool or premium | per sq yd | $45.00 – $100 |
| Carpet padding | per sq ft | $0.40 – $1.20 |
| Tack strip | per lf | $0.30 – $0.80 |
| Installation | per sq yd | $5.00 – $12.00 |
| Furniture moving | per room | $25.00 – $75.00 |
| Old carpet removal and disposal | per sq yd | $2.00 – $5.00 |
Padding is where people economise and should not. Good padding roughly doubles the life of the carpet above it, and replacing it later means pulling up the carpet again.
What goes wrong on this job
- Give the installer room dimensions, never just the area. Carpet quantity depends on how the room fits a 12 ft roll, and two rooms of identical area can differ by 40% in carpet bought.
- Ask whether the style comes in 15 ft width. On rooms between 12 and 15 ft across, a wider roll can be cheaper overall even at a higher price per yard, and it removes the seam entirely.
- Plan seams before ordering, not on the day. Seams belong along the room length, out of doorways and away from the sightline as you walk in.
- Buy new padding. Old padding is permanently compressed along the traffic paths and will telegraph the previous wear pattern straight through a new carpet.
- Check the pile direction is consistent across strips. Carpet reflects light differently with the nap, and two strips laid opposite ways look like two different colours under a window.
Frequently asked questions
How many square feet are in a square yard of carpet?
Nine. Carpet is usually priced per square yard in North America, so a $30 per square yard carpet is $3.33 per square foot.
How wide is a roll of carpet?
Twelve feet for almost all residential carpet, with 15 ft available in some styles and 13 ft 2 in on some imported goods.
How much carpet waste should I expect?
Anywhere from 0% to over 80%, entirely depending on how your room dimensions fit the roll width. A 12 ft wide room wastes nothing; a 13 ft wide room needs two strips.
How much carpet do I need for a 12x12 room?
144 square feet, which is 16 square yards, with no waste — a 12 ft room is exactly one roll width. This is why 12 ft rooms are the cheapest to carpet.
Can I reuse my old carpet padding?
You can, but it is a false economy. Padding compresses permanently along traffic paths, so new carpet over old padding wears into the same lines and feels flat where it matters.