Carpet Calculator
This carpet calculator estimates carpet two ways: by area in square yards with waste, and by roll length for the roll width you pick. Add each room as length × width, choose a 12 ft, 15 ft or 13 ft 6 in roll, and switch to Rooms and stairs to add a straight stair. It also shows the strips, the seams, the roll waste and an estimate of the pad.
Quick answer: square yards = area in sq ft × (1 + waste) ÷ 9, rounded up to the next 1/4 sq yd. A 15 × 12 ft room is 180 sq ft, which is 20 sq yd, so order 22 sq yd with 10% waste. On a 12 ft roll the same room is one strip 15 ft long: 15 linear feet.
Carpet is sold by the square yard, and cut from a roll of fixed width. By area, add up length × width for each room in square feet, add about 10% for waste, divide by 9 and round up to the next 1/4 square yard. On a roll you buy length, not area: a room is cut in strips as wide as the roll, so the width of the roll sets how many feet you buy.
Example: a 15 × 12 ft room is 180 sq ft, which is 20 sq yd. With 10% waste it is 198 sq ft, or 22 sq yd. On a 12 ft roll, the 12 ft side fits across the roll, so it is one strip 15 ft long: 15 linear feet, no seams.
Method
How this calculator works
The area method is exact arithmetic plus an allowance. The roll method shows what the width of the roll does to what you actually buy, and that often matters more than the waste percentage.
Area method
Net area is the sum of length × width for every room, and for a stair when you include one. Waste is added, the total is divided by 9 because a square yard is 3 ft × 3 ft, and the answer is rounded up to the next 1/4 square yard.
Net area = Σ (Length × Width) + Stair areaSquare yards = Net area × (1 + Waste ÷ 100) ÷ 9, rounded up to 1/4Roll method
Carpet is cut from a roll of fixed width, so you buy length. For each room the calculator tries both ways of laying the rectangle on the roll. Strips are the side across the roll divided by the roll width, rounded up, and each strip is as long as the other side plus the trim allowance. The way with fewer linear feet wins, and a tie goes to fewer seams. The stair is one run of strips cut along the roll.
Strips = round up (Side across the roll ÷ Roll width)Linear feet = Strips × (Side along the roll + Trim)Seams = Strips − 1, room by roomRoll widths
Shaw says most carpet is made in 12 ft rolls and that 15 ft rolls are available as well. BuildDirect names 12 ft, 15 ft and 13 ft 6 in, and the U.S. Department of Veterans Affairs guide specification 09 68 00 lists selectable minimum usable widths of 15, 13.5, 12 and 6 ft. The specification says usable width, so the real width is a little under the nominal one, and the maker's spec sheet wins. A room as wide as the roll shows a warning for that reason.
Roll width = 12 ft (default), 15 ft, 13 ft 6 in or your ownWaste, rounding, trim and pad
This Old House says to multiply the square footage by 0.1 and add it, and Bob Vila says to add about 10 percent, so 10% is the default. Flooring Clarity gives 5 to 10% for solid or random patterns and 10 to 15% for patterns and directional pile. Rounding up to the next 1/4 sq yd follows the Flooring Clarity note that suppliers round to a quarter or half yard. The trim allowance, 0 by default, and the pad estimate, which equals the room area, have no source and are labeled that way.
Pad area = room area (unsourced assumption)Carpet on stairs
A straight stair uses one length of carpet over every tread and riser, plus a nose allowance on each tread. Bob Vila gives an extra inch or two for the nose, so the default is 2 in, and you can edit it. The area is that length times the stair width. The risers and treads come from your stair: n risers have n − 1 treads when the top floor is the last step. Landings, bullnose steps and turns are not computed.
Stair length = Treads × (Tread depth + Nose) + Risers × Riser heightStair area = Stair length × Stair widthRoll widths and where they come from
| Roll width | In the calculator | What the sources say |
|---|---|---|
| 12 ft | Default | Shaw: most carpet is made in 12 ft rolls. BuildDirect: a lot of carpeting is laid out in 12 ft rolls. |
| 15 ft | Listed | Shaw: 15 ft rolls are available as well. Also named by BuildDirect and the VA guide specification. |
| 13 ft 6 in | Listed | Named by BuildDirect, Flooring Clarity and the VA guide specification. |
| Custom width | Listed | For any other width, such as a 6 ft commercial or narrow roll, which the VA specification also lists. |
What each field does
| Field | What to enter |
|---|---|
| What are you carpeting? | Rooms (length × width) or Rooms and stairs (the rooms plus a straight stair). |
| Rooms: Length and Width | One row per room, closet or hall, in feet and inches in the US view or meters and centimeters in the metric view. Use Add room for more, up to 20. |
| Roll width | 12 ft (the default), 15 ft, 13 ft 6 in or Custom width. You buy the full width even for a narrower room. |
| Custom roll width | Used with Custom width. The default is 12 ft. |
| Waste (area method) | 10% by default, from 0 to 50. It is a typical allowance, not a standard. Patterned or directional pile often needs more. |
| Trim allowance per strip | Extra length added to each strip, 0 by default. It is not sourced, so ask your installer. |
| Extra roll length (roll method) | An optional margin on the roll length, 0% by default, because the roll-width waste is already counted. |
| Treads, Risers, Tread depth, Riser height, Stair width, Nose allowance per tread | Only with Rooms and stairs. The defaults are 13 treads, 14 risers, a 10 in tread, a 7.5 in riser, a 36 in wide stair and a 2 in nose allowance per tread. The stair calculator finds the risers and treads from a total rise. |
What the results mean
| Result | What it is |
|---|---|
| Carpet to order, with waste | The headline answer in square yards (yd²): net area plus waste, divided by 9, rounded up to the next 1/4 yd². |
| Net area, Net area in square yards, Area to order, with waste | The rooms (and the stair) before and after waste, in ft² and yd². |
| Stairs, with waste | Rooms and stairs only: the stair carpet with the same waste, in yd². |
| Roll length to buy, Strips, Seams | The roll method for the width you chose: linear feet rounded up to the foot, how many strips, and how many seams. |
| Carpet bought on the roll, Roll waste | Roll length × roll width in yd², and the difference from the net area in ft². This is what the width of the roll costs you. |
| Pad (cushion) area | Estimated as the room area, an unsourced assumption. It does not include the stair. |
| Roll length at other widths | The linear feet for the 12 ft, 15 ft and 13 ft 6 in rolls side by side, so you can compare the price per yd². |
Worked example: a 15 × 12 ft room
Arithmetic checkedThese are the calculator's own example values: one room, a 12 ft roll, 10% waste, no trim allowance and no extra roll length.
| Step | Math | Result |
|---|---|---|
| Net room area | 15 × 12 | 180 sq ft = 20 sq yd |
| Area with waste | 180 × (1 + 10 ÷ 100) | 198 sq ft |
| Carpet by area | 198 ÷ 9 = 22, rounded up to 1/4 yd² | 22 sq yd |
| 12 ft side across the roll | ceil(12 ÷ 12) = 1 strip × 15 ft | 15 linear ft, 0 seams |
| 15 ft side across the roll | ceil(15 ÷ 12) = 2 strips × 12 ft | 24 linear ft, 1 seam |
| Roll length to buy | the smaller of the two | 15 ft |
| Carpet bought on the roll | 15 × 12 ÷ 9 | 20 sq yd, roll waste 0 |
| Other roll widths | 15 ft roll: 1 strip × 12 ft; 13 ft 6 in roll: 1 strip × 15 ft | 12 linear ft and 15 linear ft |
| Pad | room area | 180 sq ft |
| You would see | 22 sq yd to order, 15 ft off a 12 ft roll | |
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
The area formula is simple. What changes the order is the roll width, the room shape and how much pattern, pile direction and stairs you have.
The roll width can matter more than the waste
A 14 × 13 ft room is 182 sq ft, which is 22.25 sq yd with 10% waste. On a 12 ft roll it takes 2 strips of 13 ft, so 26 linear feet, which is 34.67 sq yd bought, with 130 sq ft of roll waste and 1 seam. On a 15 ft roll it takes 1 strip of 13 ft, so 13 linear feet. On a 13 ft 6 in roll it takes 14 linear feet. Compare the price per sq yd of each width.
You buy the full width
A room narrower than the roll still costs the whole roll width. That is why the roll method can be higher than the area method for a small room, and lower when the width fits well.
Rooms and stairs together
Add the default stair to the 15 × 12 ft room. The stair is 13 × (10 + 2) + 14 × 7.5 = 261 in, or 21.75 ft, times 3 ft wide, which is 65.25 sq ft. The total is 245.25 sq ft, so 30 sq yd with waste. On a 12 ft roll that is 15 + 21.75 = 36.75, so 37 linear feet in 2 strips with no seams.
The stair needs the 14th riser
A shortcut of 13 identical steps of tread, riser and nose gives 13 × 19.5 in, or 63.4 sq ft for a 3 ft stair. It misses the 14th riser. The stair formula counts risers and treads separately, and the example above is 65.25 sq ft.
Pattern, pile and seams
All strips run the same pile direction, so one strip cannot be turned. Patterned or directional carpet often needs 10 to 15% more, and pattern repeat adds more. Keep seams away from doorways and focal points. The calculator does not compute pattern repeat.
Pad and metric view
Pad is estimated as the room area, which is an unsourced assumption, so check the pad maker's instructions. In the metric view rooms are in meters and the default room is 4.5 × 3.6 m. The roll widths keep their labels 12 ft, 15 ft and 13 ft 6 in, and the lengths in the results are shown in meters.
The retailer or installer measures the room and plans seams, pattern repeat and pile direction before you order. Roll widths, waste and allowances here are typical guidance, not a standard. The calculator quotes no prices, and bullnose steps, landings and stair turns are not computed.
Common mistakes
Ordering the exact room area
Cuts, walls that are not square and seams use carpet. Typical guidance adds about 10%, and the area method does that for you.
Dividing square feet by 3
A square yard is 3 ft × 3 ft, which is 9 square feet. Divide by 9. The guide on square feet to square yards has a table.
Forgetting that you buy the full roll width
A 13 × 14 ft room on a 12 ft roll takes 26 linear feet, not the 15 or 16 you might guess from the area. Compare roll widths before you decide.
Leaving out a riser on the stairs
A stair with 14 risers has 13 treads when the top floor is the last step. Count the risers and the treads separately, and add the nose allowance to each tread.
Treating a patterned carpet like a plain one
Pattern repeat and pile direction mean more waste, and strips cannot be turned. Ask the retailer about the repeat before you order.
Questions people ask
How do I calculate how much carpet I need?
Multiply length by width for each room in feet and add the rooms. Add about 10% for waste, divide by 9 to get square yards, and round up to the next quarter yard. The guide on how to measure for carpet works the steps and the roll widths by hand.
How many square feet are in a square yard?
Nine, because a yard is 3 feet on each side. Divide square feet by 9 to get square yards. A 15 × 12 ft room, 180 sq ft, is 20 sq yd.
How much extra carpet should I buy?
Typical guidance is about 10%. Flooring Clarity gives 5 to 10% for solid or random patterns and 10 to 15% for patterned or directional carpet. Change the Waste field to match your job.
What width does carpet come in?
Most broadloom is made in 12 ft rolls, and 15 ft and 13 ft 6 in rolls are also common. Check the actual width of the product you like, since the usable width is a little under nominal.
How much carpet do I need for a 12 × 15 ft room?
By area it is 20 sq yd, so 22 sq yd with 10% waste. On a 12 ft roll it is one strip of 15 ft, so 15 linear feet with no seam.
How much carpet do I need for stairs?
The default stair of 14 risers, 13 treads, a 10 in tread, a 7.5 in riser and a 36 in width is 65.25 sq ft, or 7.25 sq yd, and 7.98 sq yd with 10% waste. See how to measure stairs for carpet, and find the risers with the Stair Calculator.
Does the calculator include the pad?
It shows a pad area equal to the room area, as an assumption with no source. Check the pad maker's instructions for how much you need.
Related calculators and guides
Sources
Where the numbers come from
- Shaw Floors, carpet installation planning most carpet in 12 ft rolls, with 15 ft rolls available, accessed October 17, 2026.
- BuildDirect, how to measure your room for carpeting 12 ft, 15 ft and 13 ft 6 in rolls, and seam placement, accessed October 17, 2026.
- U.S. Department of Veterans Affairs, guide specification 09 68 00 minimum usable broadloom widths of 15, 13.5, 12 and 6 ft, and strips laid with the pile in the same direction, accessed October 17, 2026.
- Flooring Clarity, carpet roll sizes 9 square feet per square yard and rounding up to the next quarter or half yard (editorial), accessed October 17, 2026.
- Flooring Clarity, how to measure carpet accurately 5 to 10% waste, and 10 to 15% for patterns and directional pile (editorial), accessed October 17, 2026.
- This Old House, how to measure for carpet replacement adding 10% to the total square footage, accessed October 17, 2026.
- Bob Vila, how to measure stairs for carpet rise and run per stair, an inch or two for the nose, and about 10 percent extra (editorial), accessed October 17, 2026.
- NIST Handbook 44 (2026), Appendix C exact unit conversions, including the yard and the foot, accessed October 17, 2026.