Square Foot Calculator: How Many Sq Ft?

This calculator works out the area of a rectangular space in square feet. You enter the length and width in feet (or inches, or any mix of units), and it returns the total square footage. It also shows the area in square meters for convenience.

Formula

The formula for square footage of a rectangle is:

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

Where:

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

If you measure in inches, convert to feet first by dividing by 12. For example, 6 inches = 0.5 ft. If you measure in meters, multiply by 3.281 to get feet.

Worked Example

Using the default values from the calculator: Length = 12 ft, Width = 10 ft.

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

The area is 120 square feet. The calculator also shows 11.15 square meters (120 × 0.092903 = 11.148, rounded to 11.15).

When to Use a Square Foot Calculator

Square footage is the standard unit for real estate, flooring, paint, and HVAC sizing in the United States. You might need it when:

• Comparing apartment or house sizes.
• Buying flooring, tile, or carpet (you usually need to add 10% extra for waste).
• Estimating paint coverage (one gallon covers about 350 sq ft of wall).
• Determining the size of an air conditioner or heater (roughly 20 BTU per sq ft).
• Calculating the cost of materials per square foot.

For irregular spaces, break the area into rectangles and add them together. For a triangle, use (base × height) ÷ 2.

How to Measure Correctly

Accurate measurement matters more than the math. Follow these steps:

1. Use a tape measure or laser measure. For large rooms, a laser is more accurate.
2. Measure at floor level, because walls may be slightly uneven.
3. Measure to the nearest inch (or 0.1 ft).
4. For a room that is not a perfect rectangle, divide it into rectangles and measure each separately.
5. Record measurements in feet and inches. Convert inches to feet by dividing by 12.

Example: A room is 10 ft 6 in by 8 ft 3 in. Convert: 6 in = 0.5 ft, 3 in = 0.25 ft. So length = 10.5 ft, width = 8.25 ft. Area = 10.5 × 8.25 = 86.625 sq ft.

Common Mistakes and Misconceptions

• Mixing units: Multiplying feet by inches gives nonsense. Always convert to the same unit.
• Forgetting to divide inches by 12: 12 inches × 12 inches = 1 sq ft, not 144 sq ft. Actually 12 in × 12 in = 144 sq in, which equals 1 sq ft.
• Confusing area with perimeter: Perimeter is the distance around, area is the surface. They are not interchangeable.
• Rounding too early: Round only at the end, not during intermediate steps.
• Assuming square feet = square yards: 1 sq yd = 9 sq ft. Carpet is often sold by the square yard.

A common misconception: “I have a 10×10 room, so it’s 100 square feet.” That’s correct. But “10×10” in feet is 100 sq ft, while “10×10” in inches is only 0.69 sq ft. Always check the unit.

Limits of the Formula

This formula works only for rectangles. For circles, use π × r². For triangles, use ½ × base × height. For oddly shaped rooms, the rectangle method is an approximation; you may need to hire a professional for exact measurements, especially for real estate listings.

Also, square footage does not account for height. For volume (cubic feet), you would multiply length × width × height. For wall area, you multiply wall height × wall length, and subtract windows/doors.

Square Feet vs. Other Units

Here are common conversions:

• 1 sq ft = 144 sq in
• 1 sq ft = 0.092903 sq m
• 1 sq yd = 9 sq ft
• 1 acre = 43,560 sq ft
• 1 sq m = 10.7639 sq ft

When buying materials, always check the unit on the package. For example, a box of laminate flooring may cover 20 sq ft, so you would need 120/20 = 6 boxes for a 120 sq ft room (plus extra for waste).

Frequently Asked Questions

How do I calculate square feet from inches?

Convert inches to feet by dividing by 12, then multiply length by width. For example, 24 in × 36 in becomes 2 ft × 3 ft = 6 sq ft. Alternatively, multiply inches together and divide by 144.

What is the difference between square feet and feet?

Feet measure length (one dimension), while square feet measure area (two dimensions). A room 10 ft by 10 ft has a perimeter of 40 ft but an area of 100 sq ft.

How many square feet is a 20×20 room?

400 square feet. Multiply 20 by 20. That’s roughly the size of a two-car garage.

How do I calculate square feet for a triangle?

Measure the base and the height (the perpendicular distance from the base to the opposite corner). Multiply them together and divide by 2. For example, base 10 ft, height 8 ft gives 40 sq ft.

Do I need to add extra for waste when buying flooring?

Yes. Standard practice is to add 10% for straight layouts and 15-20% for diagonal or patterned installations. For a 120 sq ft room, buy at least 132 sq ft of material.

How does square footage affect home value?

Generally, larger square footage increases value, but location, condition, and layout matter more. Appraisers use comparable sales, not just size.

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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 area_m | Area | sq m | l * w * 0.092903 | 2