Square Feet Calculator: Formula & How to Use It

This square footage calculator works out the area of a room or space in square feet (ft²) when you enter its length and width in feet, inches, or a mix of both. It returns the total area in square feet, and also shows the area in square yards and square meters for convenience. Simply enter the dimensions of any rectangular space—a room, a house, a garden, or a piece of land—and the calculator does the rest.

Formula

The formula for square footage is the same as the formula for the area of a rectangle:

Area (ft²) = Length (ft) × Width (ft)

Where:

• Length – the longer dimension of the space, measured in feet (ft).
• Width – the shorter dimension, also in feet (ft).
• Area – the resulting square footage, in square feet (ft²).

If your measurements are in inches, first convert them to feet by dividing by 12. For example, 72 inches ÷ 12 = 6 feet. If you have a measurement like 12 feet 6 inches, convert the inches to feet (6 ÷ 12 = 0.5 ft) and add it to the feet: 12.5 ft.

Worked Example

Using the default values from the calculator above (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 ft².

The calculator gives 120.00 sq ft, which matches. To convert to square yards, divide by 9 (since 1 yd² = 9 ft²): 120 ÷ 9 = 13.33 yd². To convert to square meters, multiply by 0.09290304: 120 × 0.09290304 = 11.15 m².

Why Square Footage Matters

Square footage is the standard unit of area for real estate, construction, and interior design in the United States and Canada. It is used to:

• Determine the size of a home or apartment for listing and appraisal.
• Estimate how much flooring, tile, or carpet you need to buy.
• Calculate the amount of paint for walls (though that also requires ceiling height).
• Compare the cost per square foot of different properties.
• Check if a piece of furniture will fit in a room.

In most other countries, area is measured in square meters (m²). One square meter equals about 10.764 square feet, so to convert m² to ft², multiply by 10.764.

How to Measure a Room for Square Footage

For a simple rectangular room, follow these steps:

1. Clear the area along the walls so you can run a tape measure straight.
2. Measure the length of the room from wall to wall, in feet and inches.
3. Measure the width from the opposite walls, also in feet and inches.
4. Convert any inches to decimal feet (divide by 12).
5. Multiply length × width to get the square footage.

For example, a room that is 15 feet 6 inches long and 12 feet 3 inches wide:
15 + (6/12) = 15.5 ft; 12 + (3/12) = 12.25 ft; 15.5 × 12.25 = 189.875 ft², or about 190 ft².

Irregular Shapes and Multiple Rooms

Not every space is a perfect rectangle. For L-shaped rooms, divide the space into two rectangles, calculate each area, and add them together. For a triangular area (like an attic corner), use the formula: Area = (base × height) / 2, where height is measured perpendicular to the base.

For a whole house, measure each room separately and sum the areas. Include closets and hallways if you want the total living area, but be aware that some real estate listings exclude unfinished basements, garages, and porches. Always check the local convention for what counts as “livable” square footage.

Common Mistakes and How to Avoid Them

• Mixing units: Always convert inches to feet before multiplying. If you multiply 12 ft by 6 inches, you get a meaningless 72 ft-inches, not 72 ft².
• Forgetting to round: For construction, round up to the nearest whole square foot to ensure you have enough material. For real estate, round to the nearest square foot as well.
• Measuring the outside vs. inside: For a house, exterior dimensions give the gross area, while interior dimensions give the usable floor area. They can differ by several percent.
• Assuming all walls are straight: If a wall is bowed or the room is not a perfect rectangle, measure at several points and use the average, or divide into smaller rectangles.

Limitations of the Simple Formula

The length × width formula assumes a perfect rectangle with 90-degree corners. Real rooms have doorways, alcoves, and irregular angles. For such spaces, the simple formula gives an approximation, not an exact area. For professional purposes (like a real estate appraisal), a laser measure or a professional measurement may be needed.

Also, the calculator does not account for waste. When buying flooring or tile, add 5–10% extra to cover cutting, mistakes, and future repairs. For carpet, add about 10% for seams and waste.

Frequently Asked Questions

How do I convert square feet to square yards?

Divide the square footage by 9. Since 1 yard = 3 feet, 1 square yard = 3 × 3 = 9 square feet. For example, 270 ft² ÷ 9 = 30 yd².

How do I convert square feet to square meters?

Multiply the square footage by 0.09290304. This is the exact conversion factor (1 ft = 0.3048 m, so 1 ft² = 0.3048² = 0.09290304 m²). For example, 500 ft² × 0.09290304 = 46.45 m².

What is the difference between square feet and feet?

Feet measure length (one dimension), while square feet measure area (two dimensions). A room that is 10 feet by 10 feet has an area of 100 square feet, not 100 feet. You cannot convert directly between them without knowing the other dimension.

How many square feet is a 12×12 room?

A room that is 12 feet long and 12 feet wide has an area of 144 square feet (12 × 12 = 144). This is a common size for a small bedroom or office.

Does the formula work for circular or triangular spaces?

No. For a circle, use Area = π × radius². For a triangle, use Area = (base × height) / 2. The length × width formula only works for rectangles and squares.

Should I measure in feet or inches?

Either works, but you must convert to the same unit before multiplying. Most people measure in feet and inches, then convert the inches to decimal feet. Alternatively, measure everything in inches and divide the result by 144 to get square feet (since 1 ft² = 144 in²).

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in length | Length | ft | 12 | 0
in width | Width | ft | 10 | 0
out sqft | Area | sq ft | length * width | 2
out sqyd | Area | sq yd | sqft / 9 | 2
out sqm | Area | sq m | sqft * 0.09290304 | 2