Calculate Square Feet of a Rectangle

To calculate the square feet of a rectangle, multiply its length by its width, both measured in feet. For example, a room that is 12 feet long and 10 feet wide has an area of 120 square feet (12 × 10 = 120). This calculator does that multiplication for you and also converts results to square yards and square meters.

Formula

The area of a rectangle is given by:

Area = Length × Width

Where:

• Length (l) – the longer side of the rectangle, measured in feet (ft).
• Width (w) – the shorter side, also in feet (ft).
• Area – the result in square feet (sq ft or ft²).

If your measurements are in inches, yards, or meters, convert them to feet first (1 ft = 12 in, 1 yd = 3 ft, 1 m ≈ 3.28084 ft), then multiply. The calculator above assumes you already have both dimensions in feet.

Worked Example

Using the default values from the calculator: length = 12 ft, width = 10 ft.

1. Write down the formula: Area = Length × Width
2. Plug in the numbers: Area = 12 ft × 10 ft
3. Multiply: Area = 120 sq ft

The calculator shows 120.00 sq ft as the main result. It also gives 13.33 sq yd (since 1 sq yd = 9 sq ft, 120/9 ≈ 13.33) and 11.15 sq m (since 1 sq ft = 0.09290304 sq m, 120 × 0.09290304 ≈ 11.15).

Why Square Footage Matters

Square footage is the standard unit for floor area in the United States and Canada. It is used to describe the size of homes, apartments, rooms, and commercial spaces. Real estate listings, rental agreements, and building codes all rely on square footage. For example, a typical one-car garage is about 200–250 sq ft, while a standard 2-car garage is around 400–500 sq ft. Knowing how to compute this yourself helps you verify listings, plan furniture layouts, estimate paint or flooring needs, and compare property sizes.

How to Measure a Rectangle

To get accurate square footage, you need accurate linear measurements. Use a tape measure or laser distance measurer. Follow these steps:

1. Measure the length of the rectangle (the longest side) in feet. If the side is longer than your tape, measure in sections and add them.
2. Measure the width (the side perpendicular to the length) in feet.
3. Multiply the two numbers. If you measured in inches, divide each by 12 first.
4. If the room is not a perfect rectangle (e.g., has a bay window or closet), break it into rectangles, calculate each area, and sum them.

For example, a living room that is 18 ft 6 in long and 14 ft 3 in wide: convert to feet (18.5 ft and 14.25 ft), then multiply: 18.5 × 14.25 = 263.625 sq ft, which rounds to 264 sq ft.

Common Mistakes and How to Avoid Them

• Mixing units: Multiplying feet by inches gives nonsense. Always convert to the same unit first.
• Forgetting to convert inches: 12 ft 6 in is 12.5 ft, not 12.6 ft. Divide the inches by 12.
• Rounding too early: Round only at the end. For example, 18.5 × 14.25 = 263.625; if you round 14.25 to 14.3, you get 264.55, which is off by about 1 sq ft.
• Assuming all rooms are rectangles: For L-shaped rooms, split into two rectangles and add. For triangular sections, use 0.5 × base × height.
• Using exterior dimensions for interior area: If you need usable floor area, measure inside the walls, not from outside.

Converting Square Feet to Other Units

Sometimes you need square yards (for carpet or fabric) or square meters (for international comparisons). Here are the exact conversions:

• 1 square foot = 0.111111 square yards (divide by 9)
• 1 square foot = 0.09290304 square meters
• 1 square foot = 144 square inches
• 1 square meter ≈ 10.7639 square feet

The calculator provides the first two automatically. For instance, a 12×10 ft room is 120 sq ft, which is 13.33 sq yd and 11.15 sq m. If you are buying carpet, you would order at least 13.5 sq yd to account for waste and seams.

Limitations of the Simple Formula

The length × width formula only works for perfect rectangles (all angles 90°). Real rooms often have irregularities: alcoves, angled walls, or curved sections. For those, you need to break the area into smaller rectangles and triangles, or use more advanced methods like a digital laser measure with area calculation. Also, the formula gives the flat floor area—it does not account for wall thickness, baseboards, or sloped ceilings. For painting or tiling, you may need wall area (perimeter × height) instead of floor area. Always double-check your measurements, especially for expensive materials like marble or hardwood.

Frequently Asked Questions

How do I calculate square feet from inches?

If your length and width are in inches, divide each by 12 to get feet, then multiply. For example, a rectangle 48 inches by 36 inches becomes 4 ft × 3 ft = 12 sq ft. Alternatively, multiply the inches together to get square inches, then divide by 144 (since 1 sq ft = 144 sq in). 48 × 36 = 1728 sq in, divided by 144 = 12 sq ft.

What if the rectangle is not measured in whole feet?

Use decimals. For instance, 12 ft 6 in is 12.5 ft. Multiply 12.5 × 10 = 125 sq ft. If you have fractions like 1/4 inch, convert to decimal (0.25 in = 0.0208 ft) or use inches and convert at the end. Precision matters more for large areas.

How many square feet is a 10×10 room?

A 10×10 room is 100 square feet (10 × 10 = 100). This is a common size for a small bedroom or office. In terms of other units, that is about 9.29 square meters or 11.11 square yards.

Does the order of length and width matter?

No. Multiplication is commutative, so length × width gives the same result as width × length. However, by convention, length is the longer side and width the shorter, but the area is identical either way.

Can I use this formula for a square?

Yes. A square is a rectangle with equal sides, so area = side × side. For example, a 15 ft by 15 ft square has an area of 225 sq ft. The calculator works the same; just enter the same number for length and width.

How do I calculate square feet for a room with a closet?

Measure the main rectangle and the closet separately, then add the areas. For example, a bedroom 12 ft × 10 ft (120 sq ft) plus a closet 3 ft × 2 ft (6 sq ft) gives a total of 126 sq ft. This gives the true floor area for real estate or flooring estimates.

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in l | Length | ft | 12 | 0
in w | Width | ft | 10 | 0
out area | Area | sq ft | l * w | 2
out sq_yd | Area | sq yd | (l * w) / 9 | 2
out sq_m | Area | sq m | (l * w) * 0.09290304 | 2