Carpet Square Footage Calculator

Background.

Carpet is sold in a unit almost nobody measures in. A tape measure gives you feet and inches, a US flooring store prices broadloom by the square yard, and the carpet itself comes off a roll that is usually 12 feet wide, so the yardage on a quote depends on how the rooms are cut from that roll as well as on how big they are. Getting from a sketch of the bedrooms to a figure you can hold up against two or three quotes takes four moves: add up the floor area, take out whatever will not be carpeted, add an allowance for offcuts and trimming, and convert to the seller's unit.

Each move is simple arithmetic, and together they explain why a quote rarely matches length times width. Two bedrooms of 12 × 15 and 10 × 11 feet have 290 square feet of floor between them. With a 10% allowance the purchase quantity is 319 square feet, or 35.44 square yards. Cut from a 12-foot roll, the carpet actually bought is 330 square feet, or 36.67 square yards — $1,173.33 at $32 a yard, against $1,031.11 if you priced the bare floor.

The allowance exists because broadloom cannot be poured into a room. Every piece in a room has to run with its pile in the same direction, or the seam shows as a change of shade where light catches the fibres differently. Pieces are cut a little long so they can be trimmed to the wall. Where a room is narrower than the roll, the strip beyond the wall is left over; where it is wider, a seam and a fill strip are needed, and the fill has to come from somewhere. Patterned carpet adds the cost of matching the repeat across each seam.

You can enter up to three rectangular areas in feet — rooms, a hallway, a walk-in closet — subtract built-ins or a hearth, choose a waste allowance between 0 and 50%, and price the result per square yard or per square foot. Give a roll width and you also get a linear length: each room is cut into full-width strips, in whichever direction needs less roll, and the strip lengths are added up with the waste allowance on top. It is a material estimate, not an installer's cut plan, because it does not match patterns, place seams or reuse offcuts between rooms, and the cost covers only what your unit price covers.

What is carpet square footage calculator?

Carpet square footage is the floor area that will actually be covered, found by multiplying the length and width of each rectangular area and adding the results. An irregular room is handled by splitting it into rectangles: an L-shaped bedroom becomes the main room plus the leg. What you buy is larger. The purchase area is the net floor area scaled up by a waste allowance, then usually restated in square yards, because that is how most US retailers price broadloom; one square yard is exactly 9 square feet, since a yard is exactly 3 feet. Linear feet is a third description of the same material: the length of roll, at a given width, needed to cut the rooms from full-width strips. A 12-foot roll sold 10 linear feet long holds 120 square feet, which is 13.33 square yards.

How to use this calculator.

1. 01Measure each room wall to wall at its longest length and widest width and enter them as Room 1 length and Room 1 width. The fields take decimal feet, so divide inches by 12 and round up to the next tenth: 11 ft 6 in is 11.5, and 14 ft 4 in becomes 14.4.
2. 02Use Room 2 and Room 3 for other spaces getting the same carpet, such as a second bedroom, the hallway or a closet floor. Leave both of a room's dimensions at 0 to skip it; a room with only one of its two dimensions filled in will not calculate.
3. 03In Excluded area, enter in square feet anything inside those rectangles that will not be carpeted — a raised hearth, a built-in cabinet or window seat, an island in a combined room. Leave small jogs and doorway recesses in, because they still have to be cut around.
4. 04Set Carpet roll width to the width of the product you are pricing, which is 12 ft for most US broadloom; the spec sheet or sample tag will say if a style is made wider. Leave it at 0 if you only want area; the cost is then worked out on the waste-adjusted area.
5. 05Enter a Waste allowance. 10% is a common starting point for plain carpet in a few rectangular rooms; go higher for patterned carpet, many small spaces, or rooms wider than the roll.
6. 06Choose the Price unit that matches your quote, per square yard or per square foot, and type the Unit price. Use the price of the carpet alone unless you deliberately want pad or installation folded in.

The formula.

The net area is N = Σ(Lᵢ × Wᵢ) − X, summed over the one to three rectangles you entered, where X is the excluded area in square feet. The exclusion comes off the total once, so it does not matter which room the hearth sits in, but it has to be smaller than the total or there is nothing left to carpet.

The purchase area is P = N × (1 + w), where w is the waste percentage divided by 100; a 10% allowance multiplies by 1.10. Because it is a percentage, the allowance scales with the job — a 60 sq ft hallway gets 6 sq ft extra and a 600 sq ft basement gets 60. Square yards are P ÷ 9. The linear length is worked out room by room from strips. With R the roll width in feet, a room L ft long and W ft wide can be laid with strips running along L, which takes ceil(W ÷ R) strips of length L, or with strips running along W, which takes ceil(L ÷ R) strips of length W. The calculator takes whichever needs less roll, adds the rooms, and multiplies by (1 + w). The excluded area does not shorten any strip, because a built-in cannot be cut out of the roll. Cost is priced on the carpet bought, B = linear feet × R, or B = P when no roll width is entered: (B ÷ 9) × price when the price is per square yard, or B × price when it is per square foot, and the two agree exactly when the yard price is nine times the foot price.

Area and square yards are proportional to the net area, and the waste percentage moves every output by the same factor; the strip length and the cost move in steps, because strips are whole widths of roll. The linear length is a sum over rooms, so runs are still additive: with five rooms, enter three, then the other two, and add the results, as long as the allowance, roll width and price are the same and the excluded area goes into only one run.

The linear length is still an estimate. Each room is cut on its own, so an offcut from one room is never used in another, and pile direction, pattern repeats and the position of seams are not modelled. A 13 × 15 ft room shows what the strip plan changes: area alone would give 195 × 1.10 = 214.5 sq ft, or 17.88 linear feet of 12-foot roll, but one side of the room is wider than the roll in either direction. Two strips are needed whichever way the roll runs, 2 × 15 = 30 ft one way or 2 × 13 = 26 ft the other, so the calculator uses 26 ft, which is 28.6 ft with the 10% allowance (26 ft of 12-foot roll is 312 sq ft before the allowance). The cost is priced on that roll, 28.6 ft × 12 ft = 343.2 sq ft, not on the 214.5 sq ft the area method gives, so a room wider than the roll is no longer under-priced; for the real cut plan, get the installer's measure.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute of Standards and Technology (2026). NIST Handbook 133, Appendix E: General Tables of Units of Measurement. U.S. Department of Commerce.
2. [2]National Institute of Standards and Technology (2008). Guide for the Use of the International System of Units (SI), NIST Special Publication 811. U.S. Department of Commerce.
3. [3]Bureau International des Poids et Mesures (2019). The International System of Units (SI Brochure), 9th edition. BIPM.
4. [4]The Carpet and Rug Institute (2024). Installation Standards. CRI.
5. [5]The Carpet and Rug Institute (2024). CRI 104 Commercial Carpet Installation Standard. CRI.