Carpet is the one floor covering you cannot simply buy by the square foot. It comes off a roll of fixed width, every strip must run in the same direction so the pile matches, and installers seam the strips together side by side. This calculator lays out the strips for your room in both directions, picks the one that uses the least carpet (or the direction you choose), and reports the carpet to buy in square feet and square yards along with seams, pad, tack strip and cost.
How to use the carpet calculator
- Choose US or Metric units.
- Enter the room’s length and width.
- Pick the roll width offered for the carpet you like, usually 12 ft.
- Leave Strip direction on automatic, or choose the direction you want the seams to run.
- Check the trim allowance, the extra length added to every strip.
- Tick Include pad and add prices if you want a cost estimate.
Carpet formulas
Dividing square feet by 9 gives square yards, the unit many carpet stores still quote. The calculator tries both orientations because a room that is wider than the roll in one direction may fit within it in the other.
Worked example: an 18 × 14 ft family room
Room: 18 × 14 = 252 ft² (28 yd²).
Strips running along the 14 ft side: ⌈ 18 ÷ 12 ⌉ = 2 strips, each 14 ft + 6 in = 14.5 ft.
Carpet: 2 × 14.5 ft × 12 ft = 348 ft² = 38.67 yd², with one seam. The other direction would take 444 ft².
Pad: 252 × 1.05 = 264.6 ft². Tack strip: 64 ft of perimeter, less doorways.
The same room cut from a 15-foot roll needs a single 18 ft 6 in strip: 277.5 ft² (30.83 yd²), no seam and only about 9% waste. Whenever a room is a little wider than 12 feet, ask whether the carpet you like is made in a wider roll.
Seams and layout
Seams are the weak point of a carpet installation. Installers try to:
- Point seams toward the main window, so daylight runs along the seam instead of across it, which makes the seam far less visible.
- Keep seams out of traffic lanes and doorways, where foot traffic wears and opens them.
- Run the pile the same way in every strip, and usually toward the room’s main entrance, so the color looks uniform.
- Use offcuts for closets, provided the pile direction still matches.
Because of these rules, the cheapest layout is not always the one an installer chooses. Use the direction setting to compare.
Buying and installation tips
| Item | How it is estimated |
|---|---|
| Carpet | Roll width × total strip length |
| Pad (cushion) | Room area + about 5% |
| Tack strip | Room perimeter, minus doorways |
| Transition strips | One per doorway to another floor type |
Professional installation is often priced per square yard of carpet bought, so the waste in an awkward room adds labor cost as well as material. Ask for the seam diagram with the quote; it shows exactly how many yards the installer plans to cut. For stairs, measure separately as described in the FAQ, and use the stair calculator if you need riser and tread sizes. Hard-surface rooms are easier to estimate with the flooring calculator, which works in boxes rather than roll widths.
Frequently asked questions
How many square yards of carpet do I need for a 12 × 12 room?
A 12 × 12 ft room is 144 ft², or 16 square yards. Cut from a 12-foot roll with about 3 inches of trim at each end, one strip 12 ft 6 in long covers it, so you would buy 150 ft², or about 16.7 square yards, with no seams.
Why do I have to buy more carpet than the room area?
Carpet comes off a roll in a fixed width, usually 12 feet. If the room is 14 feet wide, the second strip must still be cut from the full roll width, so most of it becomes offcut. Every strip also needs a few inches of extra length for trimming at the walls.
What widths does carpet come in?
Most broadloom carpet in the US is made 12 feet wide. Some styles are also available 13 ft 6 in or 15 ft wide, which can eliminate a seam in a wider room. In metric markets, 4 m and 5 m rolls are common.
How much carpet pad do I need?
Pad covers the room area once, without the pattern and roll-width waste of carpet, so buy the floor area plus about 5% for trimming. Pad seams are taped and should not line up with carpet seams.
How do I estimate carpet for stairs?
Add the tread depth, the riser height and about 2 inches to wrap the nosing, then multiply by the number of steps. With 10½-inch treads and 7½-inch risers, each step takes about 20 inches, so 13 steps need a strip about 21 ft 8 in long and as wide as the stairs.