The Carpet Calculator works out how much carpet to buy for a room in square yards, based on how carpet is actually sold: cut from a roll that is usually 12 ft or 15 ft wide. It also estimates the total cost, including pad and installation.
Carpet Calculator
How much carpet to buy for a room — square yards off a 12 ft or 15 ft roll — plus padding and total cost.
Because you buy full-width strips, the carpet you pay for is often more than the room’s floor area. The calculator runs strips along the longer side of the room to keep seams to a minimum, then shows both the carpet to buy and the room area.
Formula
Strips = ⌈short side ÷ roll width⌉
Carpet to buy = strips × roll width × long side ÷ 9 (yd²)
Total = carpet to buy × carpet price + room area × (pad + installation)
Where the short and long sides are the room’s width and length, and 9 ft² = 1 yd². Pad and installation are priced on the room area, since only the carpet is cut from a roll.
How the Calculation Works
Step 1: Work out how many roll-width strips cover the short side.
Step 2: Each strip is as long as the long side.
Step 3: Convert to square yards and apply prices.
Variables Explained
| Input | Meaning |
|---|---|
| Roll width | Width of the carpet roll — often 12 ft or 15 ft; check the product you are buying |
| Carpet price | Per square yard |
| Pad price, installation | Per square yard of floor |
Example Calculation
Room that fits one strip
Given (example prices): 15 × 12 ft room, 12 ft roll, carpet $30/yd², pad $5/yd², installation $6/yd²
Strips = 12 ÷ 12 = 1 → 12 × 15 = 180 ft² = 20 yd²
Total = 20 × 30 + 20 × (5 + 6) = $820
Room that needs a seam
Given: 15 × 14 ft room (210 ft² ≈ 23.3 yd²)
12 ft roll: 2 strips → 24 × 15 = 360 ft² = 40 yd² to buy
15 ft roll: 1 strip → 15 × 15 = 225 ft² = 25 yd² to buy, with no seam
Choosing the right roll width can make a big difference to the amount you buy.
Material Estimation Notes
- Offcuts from a second strip can sometimes fill closets or small areas; the calculator doesn’t reuse them.
- Patterned carpet needs extra for pattern matching.
- Stairs, closets and doorways are measured and added separately.
- Carpet pile should run the same direction across seams.
Frequently Asked Questions
How do I calculate carpet square yards?
Multiply length × width in feet and divide by 9 — then adjust for full roll-width strips.
How much carpet do I need for a 12 × 12 room?
With a 12 ft roll, one strip 12 ft long: 144 ft² = 16 yd².
Why do I have to buy more carpet than my room size?
Carpet comes in fixed roll widths, so you buy whole strips and trim the excess.
How do I convert square feet to square yards?
Divide by 9.
Is carpet pad measured the same way?
In this calculator pad is priced on the room area, since it is cut to fit.