Carpet Square Footage Calculator

This calculator works out the total square footage of carpet you need for a rectangular room. You enter the room’s length and width in feet, and it returns the area in square feet, plus the amount to order if you add a waste allowance. It also shows the area in square yards, since carpet is often sold by the square yard.

Formula

The basic formula for a rectangular room is:

Area (sq ft) = Length (ft) × Width (ft)

To convert to square yards, divide by 9 (since 1 sq yd = 9 sq ft):

Area (sq yd) = Area (sq ft) / 9

To include a waste allowance (for cuts, seams, and mistakes):

Order amount (sq ft) = Length × Width × (1 + Waste% / 100)

Variables:

• Length – the longer side of the room in feet.
• Width – the shorter side of the room in feet.
• Waste% – extra percentage added to cover trimming and pattern matching (typically 5–15%).

Worked Example

Using the default values: Length = 12 ft, Width = 10 ft, Waste = 10%.

1. Area = 12 × 10 = 120 sq ft.
2. Area in sq yd = 120 / 9 = 13.33 sq yd (rounded to 2 decimals).
3. Order amount = 120 × (1 + 10/100) = 120 × 1.10 = 132 sq ft.

The calculator shows: Carpet area = 120.00 sq ft, Carpet area = 13.33 sq yd, Order amount = 132.00 sq ft.

Why Waste Allowance Matters

Most rooms are not perfect rectangles. Doorways, closets, and alcoves add complexity. Even in a simple rectangle, you need extra carpet for:

• Trimming edges to fit the room exactly.
• Matching patterns if the carpet has a design (add 10–15% for patterns).
• Seams if the room is wider than the carpet roll (usually 12 ft wide).
• Mistakes during installation.

A standard waste allowance is 10% for straight layouts, but for patterned carpet or diagonal installation, 15% is safer.

How to Measure Your Room

Use a metal tape measure, not a cloth one, for accuracy. Measure the length and width at the widest points, and measure in feet and inches. If you have inches, convert to feet by dividing by 12 (e.g., 5 ft 6 in = 5.5 ft).

For L-shaped rooms, divide the space into two rectangles, calculate each area, and add them together. For stairs, measure the tread (horizontal part) and riser (vertical part) separately – each step is usually about 3–4 sq ft.

Common Mistakes and How to Avoid Them

• Mixing units: Always use the same unit (feet) for both length and width. If you measure in inches, convert first.
• Forgetting the waste: Ordering exactly the room area often leaves you short, especially if the room is not a perfect rectangle.
• Ignoring roll width: Carpet comes in rolls, typically 12 ft wide. If your room is wider than the roll, you’ll need a seam, which adds waste.
• Rounding too early: Keep full precision until the final answer, then round up to the nearest square foot or yard.

How to Read the Results

The first result is the exact area of the room. The second is the area in square yards – useful because many carpet retailers price per square yard. The third is the amount you should order, including waste. Always round up to the nearest whole number when ordering; you cannot buy a fraction of a square foot of carpet.

For example, if the calculator says 132.00 sq ft, order at least 133 sq ft. If you’re buying by the square yard, round 13.33 sq yd up to 14 sq yd.

Limitations of the Formula

This calculator assumes a simple rectangle. It does not account for:

• Rooms with irregular shapes – you’ll need to break them into rectangles.
• Carpet roll width – you may need more if your room is wider than 12 ft.
• Pattern matching – add extra waste for patterned carpet.
• Stairs, closets, or hallways – measure these separately and add to the total.

For complex layouts, it’s wise to have a professional installer measure the space, as they can factor in all these variables.

Frequently Asked Questions

How many square feet is a 12×12 room?

A 12×12 room is 144 square feet (12 × 12 = 144). With a 10% waste allowance, you’d order about 158 square feet.

How do I convert square feet to square yards for carpet?

Divide the square footage by 9. For example, 120 sq ft ÷ 9 = 13.33 sq yd. Carpet is often sold by the square yard, so this conversion is essential.

What is a good waste percentage for carpet?

For a simple rectangular room with no pattern, 5–10% is typical. For patterned carpet or rooms with many angles, use 15%. Always round up to the nearest full square foot or yard.

Can I use this calculator for L-shaped rooms?

Yes, but you need to divide the room into two rectangles, calculate each area separately, and add them together. Then add your waste percentage to the total.

Why is carpet sold by the square yard instead of square foot?

Historically, carpet rolls were measured in yards in the US, and the industry kept that convention. One square yard equals 9 square feet, so a 12×12 room (144 sq ft) is 16 sq yd.

Do I need to add waste for a concrete slab?

No, the waste allowance is for the carpet itself, not the subfloor. The same waste percentage applies whether you’re installing over concrete, wood, or old carpet.

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in l | Length | ft | 12 | 0
in w | Width | ft | 10 | 0
in waste | Waste % | % | 10 | 0
out area | Carpet area | sq ft | l * w | 2
out area_yd | Carpet area | sq yd | (l * w) / 9 | 2
out order | Order amount | sq ft | (l * w) * (1 + waste / 100) | 2