Figure Square Footage Calculator: How to Use It

This calculator works out the square footage of a rectangular room or area from its length and width in feet, and returns the total area in square feet. You enter the length and width (in feet, or inches, or both), and the calculator gives you the area in square feet and square yards. It uses the standard formula: area = length × width.

Formula

The formula for square footage of a rectangle is simply:

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

Where:

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

If you measure in inches, convert to feet first by dividing by 12. For example, 6 inches = 0.5 ft. If you measure in yards, multiply by 3 to get feet.

Worked Example

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

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

The calculator gives 120.00 sq ft, and 120 / 9 = 13.33 sq yd (rounded to two decimals). That matches.

Why Square Footage Matters

Square footage is the standard unit for floor area in the United States and Canada. It’s used for:

• Real estate listings: Homes are advertised by total living area.
• Flooring and tile: You need to know how much material to buy.
• Paint and wallpaper: Coverage is often given per square foot.
• HVAC sizing: Heating and cooling loads depend on area.
• Building permits: Many codes require area calculations.

Getting the number right saves money and avoids waste.

How to Measure a Room Correctly

For a simple rectangle, measure from wall to wall at the baseboard. Use a tape measure that reads in feet and inches. If the room isn’t a perfect rectangle, break it into rectangles, calculate each area, and add them together.

For example, an L-shaped room can be split into two rectangles. Measure each part’s length and width, compute each area, then sum them.

Always measure in the same unit. If you measure one side in feet and the other in inches, convert first. A common mistake is mixing units without converting, which throws off the result by a factor of 12.

Common Mistakes and How to Avoid Them

• Mixing units: Always convert to feet before multiplying. Inches to feet: divide by 12. Yards to feet: multiply by 3.
• Rounding too early: If you round each measurement to the nearest foot, you can lose accuracy. Keep inches as decimals (e.g., 12 ft 6 in = 12.5 ft).
• Forgetting closets and alcoves: For living area, include finished spaces that are heated and accessible. Unfinished basements usually aren’t counted.
• Assuming the room is a perfect rectangle: Most rooms have irregularities. Measure at several points and use the average if walls are not straight.

Square Feet vs. Square Meters

Most of the world uses square meters. To convert square feet to square meters, multiply by 0.092903. To go the other way, multiply square meters by 10.7639.

For example, a 120 sq ft room is 120 × 0.092903 = 11.15 sq m. A 20 sq m room is 20 × 10.7639 = 215.28 sq ft.

When buying flooring online from an international seller, always check which unit they use. A 10% error in conversion can mean buying too much or too little material.

Limitations of the Simple Formula

The length × width formula works only for rectangles. For circles, triangles, or irregular shapes, you need different formulas:

• Circle: Area = Ï€ × (radius²).
• Triangle: Area = ½ × base × height.
• Trapezoid: Area = ½ × (base1 + base2) × height.

Also, this calculator gives the floor area, not the wall area. For paint or wallpaper, you need to measure wall height and perimeter separately.

When to Call a Professional

For most DIY projects, a tape measure and this calculator are enough. But if you’re buying or selling a home, an appraiser or surveyor will provide an official measurement. Disputes about square footage can be significant, so professional measurement is worth it when accuracy is legally important.

Frequently Asked Questions

How do I calculate square footage of a room with irregular shape?

Break the room into rectangles, triangles, or circles. Calculate each area separately and add them together. For a triangle, use ½ × base × height. For a circle, use π × radius². For a complex shape, you can also use graph paper or a digital floor plan tool.

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 ft by 10 ft has an area of 100 square feet, but its perimeter is 40 feet. They are not interchangeable.

Does the calculator include the thickness of walls?

No, it calculates the area based on the length and width you enter. If you want the interior floor area, measure from inside wall to inside wall. For exterior dimensions, you’d get the building footprint, which is larger.

How many square feet is a 12×12 room?

A 12 ft by 12 ft room is 144 square feet (12 × 12 = 144). This is a common size for a small bedroom or home office.

Can I use this calculator for square yards?

Yes, the calculator also outputs square yards. Since 1 square yard = 9 square feet, divide the square footage by 9. For example, 120 sq ft ÷ 9 = 13.33 sq yd.

What if my measurements are in feet and inches?

Convert the inches to a decimal of a foot first. For instance, 6 inches is 0.5 ft, so 12 ft 6 in becomes 12.5 ft. Then multiply length by width. The calculator assumes you enter feet as a decimal.

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in length_ft | Length (feet) | ft | 12 | 0
in width_ft | Width (feet) | ft | 10 | 0
out area_sqft | Area | sq ft | length_ft * width_ft | 2
out area_sqyd | Area | sq yd | (length_ft * width_ft) / 9 | 2