Calculate Square Feet Formula & How to Use It

To calculate square feet, multiply the length by the width of a space, both measured in feet: Area (sq ft) = Length (ft) × Width (ft). For example, a room that is 12 feet long and 10 feet wide is 120 square feet (12 × 10 = 120). This formula gives the area of any rectangle or square, and with slight adjustments it also works for circles, triangles, and odd-shaped rooms.

Formula

The basic square footage formula is:

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

Where:

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

If your measurements are in inches, first convert them to feet by dividing by 12 (e.g., 24 inches ÷ 12 = 2 ft). If they are in yards, multiply by 3 to get feet. The formula only works when both dimensions use the same unit.

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: 12 × 10 = 120.
4. Attach the unit: 120 square feet.

The calculator returns 120.00 sq ft, matching the hand calculation.

When to Use Square Footage

Square footage is the standard unit for floor area in the United States and Canada. You will need it when:

• Buying or selling a home – listing prices are often quoted per square foot.
• Ordering flooring, tile, or carpet – materials are sold by the square foot or square yard.
• Painting walls or ceilings – paint coverage is listed in square feet per gallon.
• Installing sod or mulch – landscaping products are sold by area.
• Calculating rent or lease costs – commercial rent is often per square foot per year.

For most of these tasks, you measure the length and width of each room, multiply, and then add the areas of all rooms together to get the total living area.

How to Measure Odd-Shaped Rooms

Not every space is a perfect rectangle. For L-shaped rooms, break the space into two rectangles, calculate each area separately, and add them together. For example, an L-shaped kitchen with a 10 ft × 8 ft main area and a 4 ft × 3 ft nook has a total of 80 + 12 = 92 sq ft.

For triangular spaces, use the formula: Area = (Base × Height) ÷ 2. Measure the base (one side) and the height (perpendicular distance to the opposite corner), multiply, then divide by 2.

For circular areas (like a round patio), use Area = π × r², where r is the radius (half the diameter). If the diameter is 10 ft, the radius is 5 ft, so the area is π × 25 ≈ 78.54 sq ft.

Common Mistakes and How to Avoid Them

The most frequent errors come from mixing units:

• Using inches with feet – Always convert to feet first. A 12 ft by 10 ft room is 120 sq ft, but a 12 in by 10 in tile is only 0.83 sq ft.
• Forgetting to convert inches to feet – Divide inches by 12 before multiplying. For example, 6 inches = 0.5 ft.
• Measuring the outside instead of the inside – For floor area, measure from interior wall to interior wall, not including baseboards.
• Rounding too early – If you measure 12.3 ft and 10.7 ft, multiply the exact numbers (131.61 sq ft) rather than rounding to 12 and 11 first.
• Confusing square feet with cubic feet – Square feet measure flat area (2D); cubic feet measure volume (3D). To get cubic feet, multiply length × width × height.

Limits of the Formula

The length × width formula assumes a perfect rectangle with right angles. Real rooms often have bay windows, closets, or irregular walls. For a truly accurate floor plan, you may need to measure each segment and add them up, or use a laser distance measurer. Also, the formula gives the gross area – it does not subtract for walls, columns, or built-in furniture. When comparing property listings, check whether the square footage is “living area” (finished, heated spaces) or “total area” (including garages and basements), as definitions vary by region and listing service.

Square Feet vs. Square Meters

If your measurements are in meters, the area is in square meters. To convert square feet to square meters, multiply by 0.092903. To convert square meters to square feet, multiply by 10.7639. For example, a 120 sq ft room is about 11.15 m² (120 × 0.092903). Conversely, a 20 m² room is about 215.28 sq ft (20 × 10.7639).

When shopping for flooring or paint, always check the unit on the product label – many products list coverage in both square feet and square meters, but some only use one. Using the wrong unit can lead to buying too much or too little material.

Frequently Asked Questions

How do I calculate square feet from inches?

First convert inches to feet by dividing by 12. For example, a tile that is 12 inches by 12 inches is 1 ft × 1 ft = 1 sq ft. If your room is 144 inches by 120 inches, convert to 12 ft × 10 ft = 120 sq ft.

What is the formula for square feet of a triangle?

For a triangle, use Area = (Base × Height) ÷ 2. Measure the base (one side) and the height (the perpendicular distance from the opposite corner to that base), multiply them, then divide by 2. The result is in square feet if both measurements are in feet.

How many square feet is a 10×10 room?

A 10 ft by 10 ft room is 100 square feet (10 × 10 = 100). This is a common size for a small bedroom or home office.

Do I need to subtract for doors and windows when calculating wall area?

For painting or wallpapering, yes – subtract the area of doors and windows to avoid buying too much paint. Measure the height and width of each opening, multiply to get its square footage, and subtract from the total wall area. For flooring, you do not subtract anything; the floor is continuous.

Is square footage the same as square yards?

No. One square yard equals 9 square feet (since 1 yard = 3 feet, and 3 × 3 = 9). To convert square feet to square yards, divide by 9. For example, 120 sq ft ÷ 9 = 13.33 sq yd.

What if my room is not a perfect rectangle?

Break the room into smaller rectangles, triangles, or circles, calculate each area using the appropriate formula, and add them together. For an L-shaped room, split it into two rectangles. For a rounded alcove, treat it as a half-circle and add its area to the rectangle.

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in l | Length | ft | 12 | 0
in w | Width | ft | 10 | 0
out area | Area | sq ft | l * w | 2