How to use the carpet calculator
- Enter the room length and width.
- Enter the roll width. 12 ft is common in the US; 4 m is common in metric markets. Check with your supplier.
- Enter the trim allowance at each end of each piece, for fitting against walls.
The calculator tries strips in both directions and shows the layout that uses less carpet. Take the result to the store with your room sketch, so the fitter can check where the seams fall before cutting, as Decoratoradvice recommends.
Carpet formula
Strips = room width ÷ roll width, rounded up
Cut length = room length + 2 × trim allowance
Carpet to buy = strips × cut length × roll width
The calculator also works the other way round (strips across the length) and picks the smaller result.
Worked examples
A 15 × 12 ft room, 12 ft roll, 3 in trim each end:
One strip covers the 12 ft width
Cut length: 15 ft + 6 in = 15 ft 6 in
Carpet: 12 × 15.5 = 186 sq ft = 20.7 sq yd
A 15 × 14 ft room on the same roll needs two strips either way. Running them across the 14 ft width takes 2 × 14 ft 6 in = 29 ft of roll (348 sq ft, 38.7 sq yd), less than 2 × 15 ft 6 in = 31 ft the other way.
Tips
- Seams are best placed away from doorways and heavy traffic, with the pile running the same direction on both pieces.
- Order padding (underlay) for the room area, not the carpet area. The square footage calculator gives the room area.
- Ask whether the price is per square yard or square foot. 1 sq yd = 9 sq ft.
- Fit the baseboard afterwards or protect it; the baseboard calculator counts new trim.
Common mistakes
- Buying room area only. A 14 ft wide room on a 12 ft roll needs two full strips, so you pay for 24 ft of width.
- No trim allowance. Walls are rarely straight; fitters need extra at each end.
- Ignoring pile direction. Pieces turned the wrong way look like different colours.
Frequently asked questions
How many square yards of carpet do I need for a 12 × 12 room?
From a 12 ft roll with 3 in trim each end: 12 × 12.5 = 150 sq ft, or 16.7 sq yd.
How do I convert square feet to square yards?
Divide by 9. 180 sq ft is 20 sq yd.
What width does carpet come in?
Commonly 12 ft in the US, with some products in 15 ft or 13 ft 2 in. Check the product details.
Why is carpet more than the room size?
The roll has a fixed width, and every piece needs trim. Narrow leftovers from the roll edge are usually waste.
Is carpet cheaper than other flooring?
It depends on the products. Compare like for like by working out plank flooring with the flooring calculator and tile with the tile calculator.
Key takeaways
- You buy roll width × cut length, not room area.
- Add trim at each end of each piece.
- Try strips both ways; the calculator picks the cheaper layout.
- Padding is based on room area.