What this calculator does
Find out how much carpet and pad to buy for your rooms, and what it will cost. Carpet isn't bought by floor area alone. It comes off a roll of fixed width, usually 12 feet. So a room is covered with strips cut to length. Any part of the roll's width that the room doesn't need becomes an offcut (a leftover piece). A 15 × 14 ft room has 210 square feet of floor. But covering it from a 12 ft roll takes two strips, and you pay for the full width of both.
This calculator lays out each room the way an estimator would. It tries running the strips both ways and picks the one that uses less carpet. Then it adds a trim allowance to each strip. It shows the carpet to buy in square feet and square yards, and the length to cut from the roll. It also gives the number of seams and the pad for the floor area. Add a price per square yard to see the material cost.
Where it's used
Why this math matters outside the classroom:
- Buying carpet. A homeowner covers a 15 × 14 ft room from a 12 ft roll with 2 strips of 14.5 ft, buying 348 ft² for 210 ft² of floor.
- Quoting a job. An estimator converts 486 ft² of carpet to 54 yd² and prices it at $30 per square yard for $1,620.
- Planning seams. A room 14 ft wide needs 2 strips from a 12 ft roll but only 1 from a 15 ft roll, removing a seam.
- Rounding up in word problems. Students see why 14 ÷ 12 strips must round up to 2, since a remainder still needs a whole strip.
Grade level and standards: Grades 4–5; Common Core State Standards for Mathematics 4.MD.A.3, 4.OA.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose feet or meters and the number of rooms. Split an L-shaped room into two rectangles.
- Enter each room's length and width at its longest points. Include closets and doorways you want carpeted.
- Set the roll width (12 ft is the most common) and the trim allowance added to each strip.
- Tick pad if you need it, and add prices if you want a cost. Then read the carpet to buy, the roll length and the seam count.
What the inputs mean
- Measure in
- Use decimals for inches: 6 in = 0.5 ft, 9 in = 0.75 ft.
- Number of rooms or areas
- Split an L-shaped room into two rectangles.
- Roll width
- Ask the store which widths your chosen carpet comes in. A 15 ft roll can cover a room 13–15 ft wide without a seam. That may cost less overall, even though the roll is wider.
- Trim allowance per strip
- Strips are cut a little long so the installer can trim them to the walls. About 3 inches at each end, 0.5 ft per strip, is typical.
- Pad allowance
- Pad is laid in pieces pushed edge to edge, so it wastes much less than carpet. A small allowance covers cutting around corners and doorways.
- Carpet price (optional)
- Carpet is often priced per square yard. If your quote is per square foot, switch the unit. 1 yd² = 9 ft².
Formula and method
strips = ⌈span across the room ÷ roll width⌉ length off the roll = strips × (strip length + trim allowance) carpet to buy = total length off the roll × roll width square yards = square feet ÷ 9 pad = floor area × (1 + allowance ÷ 100) seams per room = strips − 1
The brackets ⌈ ⌉ mean round up. A room 14 ft across needs two 12 ft strips, because one strip would leave a 2 ft gap. Each strip runs the full length of the room, plus a trim allowance. The span across the room is its size measured at a right angle to the way the strips run. The allowance in the pad line is the extra percent you enter.
Each room is checked two ways: strips running along its length, and along its width. The calculator uses whichever direction takes less carpet. The carpet you buy is the total length cut from the roll times the roll width. So it includes the offcuts and trim.
Worked example
A 15 × 14 ft living room and a 12 × 11 ft bedroom are carpeted from a 12 ft roll with 0.5 ft of trim per strip. Carpet costs $30 per square yard and you want pad with a 5% allowance.
- Living room: strips along the 14 ft side need ⌈15 ÷ 12⌉ = 2 strips of 14.5 ft = 29 ft (the other way would take 31 ft).
- Bedroom: ⌈12 ÷ 12⌉ = 1 strip of 11.5 ft.
- Length off the roll: 29 + 11.5 = 40.5 ft.
- Carpet to buy: 40.5 × 12 = 486 ft², which is 486 ÷ 9 = 54 yd².
- Pad: 342 ft² of floor × 1.05 = 359.1 ft².
- Carpet cost: 54 yd² × $30 = $1,620.
Result: Buy 486 ft² (54 yd²) of carpet, cut as 40.5 ft from a 12 ft roll with one seam, plus 359.1 ft² of pad. The carpet costs about $1,620 before installation.
Understanding the result
The gap between floor area and carpet to buy is the offcut and trim. Here, 342 ft² of floor needs 486 ft² of carpet. The 144 ft² difference is about 30% of what you buy. That's mostly because the living room is just over one roll width wide. A wider roll or a different seam plan could reduce it.
The seam count matters for looks as well as cost. Installers like to keep seams away from doorways and the main line of sight. So their plan may differ slightly from the least-carpet layout here.
Assumptions and limitations
- Each room or area is a rectangle, measured wall to wall.
- Strips in one room all run the same direction and are cut from a single roll width.
- Offcuts aren't reused in other rooms or closets, so the estimate leans to the safe side.
- Patterned carpet needs extra length so the pattern lines up from strip to strip. Add it to the trim allowance or ask the retailer.
- It doesn't include stairs, oddly shaped closets or transitions (the strips where carpet meets another floor). Measure them as separate rectangles.
- Prices are what you enter. Installation, removing old carpet, tack strip (the spiked strip that holds carpet at the walls) and transitions are usually quoted separately.
Frequently asked questions
How many square yards of carpet do I need for a 12 × 12 room?
From a 12 ft roll, one strip 12 ft long plus 0.5 ft of trim covers it: 12.5 × 12 = 150 ft², or about 16.7 yd². The floor itself is 144 ft², or 16 yd².
Why is the carpet to buy more than the room's area?
Because carpet comes in fixed widths. Any part of a strip's width that runs past the wall is cut off. Each strip is also cut a little long for trimming. Rooms that are slightly wider than the roll waste the most.
Should I choose a 12 ft or 15 ft roll?
Try both in the calculator. A room 13 to 15 ft wide needs a seam from a 12 ft roll, but none from a 15 ft roll. The wider roll may also waste less. Not every carpet style comes in both widths.
How much pad do I need?
About the floor area plus a small allowance. That's because pad pieces are pushed edge to edge, not cut from full-width strips. The calculator uses the floor area plus the percentage you enter.
How this calculator is checked
Method: Strip layout from a fixed roll width (rounded-up strip count × strip length with trim), best of two directions; exact 1 ft = 0.3048 m and 1 yd² = 9 ft². The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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