Square feet of a Rectangle Calculator

Enter the length and width of a rectangular space in feet to get its area, perimeter, material needed with a waste allowance, and an estimated project cost.

Quick Facts

Formula
Area (ft²) = Length × Width
9 ft² = 1 yd²; 1 ft² ≈ 0.0929 m². Perimeter = 2 × (Length + Width).

Your Results

Calculated
Area
-
Length × Width, in ft²
Perimeter
-
2 × (Length + Width), in ft
Material to buy
-
Area plus waste allowance
Estimated cost
-
Material area × price per ft²

Ready

Enter length and width, then press Calculate.

Formula for square feet of a rectangle

The square footage of a rectangle is its length multiplied by its width, both measured in feet: Area (ft²) = Length × Width. This is the standard formula for the area of a rectangle in Euclidean geometry — it works for any room, yard, wall, or lot whose sides meet at right angles. Measure both sides in the same unit before multiplying; if you measured in inches, divide by 12 first to convert to feet.

How this calculator works

Enter the length and width of the space in feet. The calculator multiplies them to get the area, then reports four related figures: the raw area (Length × Width), the perimeter (2 × (Length + Width)) for edging or trim, the material to buy after adding your waste/overage percentage, and an estimated cost from the material quantity and your price per square foot. Set the price and waste allowance to 0 if you only need the geometric area and perimeter.

Why add a waste allowance

Flooring, tile, carpet, sod, and paint are sold in fixed-size units, and real installations lose material to cuts, seams, pattern matching, and mistakes. A common rule of thumb is to add about 10% for a simple rectangular room and 15–20% for rooms with many corners, closets, doorways, or diagonal-laid patterns. The calculator applies this percentage on top of the raw area to estimate how much material to actually purchase.

Common mistakes to avoid

  • Mixing units: area comes out in square feet (ft²) only if both length and width were entered in feet. A room that is 3 ft on each side has an area of 9 ft², not 9 ft.
  • Forgetting the waste allowance: ordering material for exactly the raw area often leaves you short once cuts and seams are accounted for.
  • Non-rectangular rooms: for L-shaped or irregular spaces, split the space into rectangles, calculate each one's area separately, and add the results together.

Real-world applications

  • Flooring, carpet, tile, and paint projects use the area plus a waste allowance to estimate how much material to buy
  • Fencing, baseboards, and edging use the perimeter to plan linear material
  • Real estate listings and rent pricing use square footage to compare properties
  • Landscaping, sod, and gravel projects use area to estimate coverage and delivery quantities

Frequently Asked Questions

What is the formula for square feet of a rectangle?
Multiply the length by the width, both measured in feet: Area (ft²) = Length × Width. For example, a room that is 12 ft by 10 ft covers 12 × 10 = 120 square feet.
How do I convert square feet to square yards or square meters?
Divide square feet by 9 to get square yards, since 9 ft² equal 1 yd². Multiply square feet by 0.0929 to get square meters, since 1 ft² is about 0.0929 m².
Why add a waste or overage percentage when ordering material?
Flooring, tile, and paint are sold in fixed-size units, and cuts, seams, and mistakes use up extra material. A common rule of thumb is to add about 10% for a simple rectangular room and up to 15-20% for rooms with many corners, closets, or diagonal patterns.
How do I find the perimeter of a rectangle?
Add the length and width, then multiply by two: Perimeter = 2 × (Length + Width). For a 12 ft by 10 ft room, perimeter = 2 × (12 + 10) = 44 ft.

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