What to measure
How to use the carpet calculator
Enter the room’s length and width and choose the roll width (most carpet is 12 ft). The calculator tries laying the strips both ways and picks the one that uses less carpet.
The formula
- Strips = room width ÷ roll width, rounded up
- Roll length = strips × (room length + 6 in for trimming)
- Carpet to buy = roll length × roll width — then the same with length and width swapped; the smaller wins
Worked example: 15 × 20 ft living room, 12 ft roll
- Strips along the 20 ft side: 2 × 20.5 ft = 41 ft of roll
- Strips along the 15 ft side: 2 × 15.5 ft = 31 ft of roll ← shorter
- 31 × 12 = 372 sq ft (41.33 sq yd) to buy for a 300 sq ft room
A wider roll can remove a seam entirely: a 14 × 13 ft room fits on one strip of 15 ft carpet (about 203 sq ft) instead of two strips of 12 ft (324 sq ft).
This calculator doesn’t plan pattern matching, closets or stairs. For patterned carpet, add 10–15% and ask the store to measure.
Carpet to buy by room size
Square feet to buy, with 6 in per strip for trimming; the calculator picks the better direction.
| Room | Room area | 12 ft roll | 15 ft roll |
|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 126 sq ft | 158 sq ft |
| 12 × 12 ft | 144 sq ft | 150 sq ft | 188 sq ft |
| 12 × 14 ft | 168 sq ft | 174 sq ft | 188 sq ft |
| 12 × 18 ft | 216 sq ft | 222 sq ft | 278 sq ft |
| 14 × 16 ft | 224 sq ft | 348 sq ft | 248 sq ft |
| 15 × 20 ft | 300 sq ft | 372 sq ft | 308 sq ft |
| 16 × 20 ft | 320 sq ft | 396 sq ft | 495 sq ft |
| 20 × 20 ft | 400 sq ft | 492 sq ft | 615 sq ft |
Common mistakes
- Buying the room’s square footage. Carpet comes in full-width strips, so you pay for the roll length times the roll width.
- Measuring at one spot. Walls are rarely straight; measure each side at its widest point.
- Forgetting closets and doorways. If the carpet runs into a closet or through a doorway, add that area to the room size.
- Planning to turn an offcut sideways to fill a gap. All strips should run the same direction, or the pile looks different at the seam.
Frequently asked questions
How much carpet do I need for a 12x12 room?
150 sq ft (16.67 sq yd). The room is 144 sq ft, but you buy a 12.5 ft length off a 12 ft roll to allow for trimming.
Why do I need more carpet than the room's square footage?
Carpet is cut in full-width strips from the roll. A 13 ft wide room on a 12 ft roll needs a second strip, and every strip needs a few inches at each end for trimming.
Is carpet sold by the square foot or square yard?
Both — stores often list price per square foot, installers and older price lists per square yard. One square yard is 9 square feet.
Do I need as much pad as carpet?
No. Pad is pieced together without seam waste, so the room's area is enough.
How much carpet do I need for a 10x10 room?
126 sq ft (14 sq yd) off a 12 ft roll — one 10.5 ft length. The room is only 100 sq ft, but the 12 ft width overhangs the 10 ft wall.
Should I buy carpet on a 12 or 15 ft roll?
Whichever covers the room's width in fewer strips. A 14 × 16 ft room needs 348 sq ft off a 12 ft roll but 248 sq ft off a 15 ft roll; a 12 × 12 ft room is the other way round, 150 against 188 sq ft.
How much carpet for a 20x20 room?
492 sq ft (54.67 sq yd) off a 12 ft roll — two strips of 20.5 ft. A 15 ft roll would take 615 sq ft, because the second strip is still needed.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.