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Construction & Home
Square Footage Calculator — Area in Sq Ft, Sq Yards & Acres
The measurement behind flooring, paint, carpet, tile and real-estate listings
Square footage is the number that decides how much flooring, carpet, tile, sod, paint or drywall you need to buy — and how much it costs. It's also how American real estate is priced, how rent is quoted per square foot, and how contractors bid a job. Get it wrong and you either run out of material halfway through or pay for boxes you'll never open.
The core formula is just length times width. Square footage = length (ft) × width (ft). A room that's 12 feet long and 10 feet wide is 12 × 10 = 120 square feet. If your flooring costs $3.50 per square foot, the material runs 120 × $3.50 = $420 before waste.
Measurements rarely land on whole feet, so the trick is converting inches first. There are 12 inches in a foot, so divide inches by 12 and add them on. A wall that's 10 ft 6 in is 10 + 6 ÷ 12 = 10.5 ft. A space 12 ft 3 in by 9 ft 6 in = 12.25 × 9.5 = 116.4 sq ft.
Other shapes use their own formulas:
• Square: side × side. • Circle: π × radius² (radius is half the diameter). A round patio 10 ft across has a 5 ft radius → 3.14159 × 5² = 78.5 sq ft. • Triangle: ½ × base × height.
Once you have square feet, two conversions show up constantly. Square yards = sq ft ÷ 9 (carpet is often priced this way), and acres = sq ft ÷ 43,560 (used for lots and land). So 120 sq ft = 13.33 sq yd, and a 0.25-acre lot is 0.25 × 43,560 = 10,890 sq ft.
The most common mistake is mixing units — multiplying feet by inches, or forgetting to convert inches before multiplying. Always get both dimensions into the same unit (decimal feet) first. The second mistake is skipping waste: flooring, tile and carpet need roughly 5–10% extra for cuts, mistakes and pattern matching, so buy a little more than the bare square footage.
This calculator handles rectangles, squares, circles and triangles, reports the area in square feet, square yards and acres, and — if you enter a price per square foot — gives you the total project cost in one shot.
📖 See also: How to Calculate a Tip (and Split the Bill)
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Rectangle / Square: area (sq ft) = length × width • Circle: area = π × radius² (radius = diameter ÷ 2) • Triangle: area = ½ × base × height • Inches to feet: feet = ft + (in ÷ 12) • Square yards = sq ft ÷ 9 • Acres = sq ft ÷ 43,560 • Total cost = sq ft × price per sq ft
📰 Formula
• Rectangle / Square: area (sq ft) = length × width • Circle: area = π × radius² (radius = diameter ÷ 2) • Triangle: area = ½ × base × height • Inches to feet: feet = ft + (in ÷ 12) • Square yards = sq ft ÷ 9 • Acres = sq ft ÷ 43,560 • Total cost = sq ft × price per sq ft
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Multiplying feet by inches without converting inches to feet first.
- Using the diameter instead of the radius in the circle formula.
- Dividing by 12 instead of 9 to get square yards (12 is for length, 9 is for area).
- Forgetting to add 5–10% extra material for cuts and waste.
💡 Tips
- Convert every inch reading to decimal feet (in ÷ 12) before you multiply.
- For odd-shaped rooms, split them into rectangles, find each area, and add them up.
- Buy about 10% more flooring than the bare square footage to cover cuts and mistakes.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/square-footage-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How do I calculate square footage?
Multiply length by width in feet. A room 12 ft by 10 ft is 12 × 10 = 120 square feet. For inches, divide by 12 first: 10 ft 6 in = 10.5 ft.
How do I find the square footage of a room with inches?
Convert inches to feet by dividing by 12, then multiply. A 12 ft 3 in by 9 ft 6 in room = 12.25 × 9.5 = 116.4 square feet.
How many square feet are in a square yard?
9 square feet make 1 square yard. To convert square feet to square yards, divide by 9. So 120 sq ft = 120 ÷ 9 = 13.33 sq yd.
How many square feet are in an acre?
An acre is 43,560 square feet. To convert square feet to acres, divide by 43,560. A 10,890 sq ft lot is 10,890 ÷ 43,560 = 0.25 acres.
How do I calculate the square footage of a circle?
Area = π × radius². The radius is half the diameter. A circle 10 ft across has a 5 ft radius, so area = 3.14159 × 5² = 78.54 sq ft.
How do I find the area of a triangle in square feet?
Area = ½ × base × height. A triangle with a 12 ft base and 8 ft height = 0.5 × 12 × 8 = 48 square feet.
How much flooring do I need for a room?
Measure the square footage, then add 5–10% for cuts and waste. A 120 sq ft room needs about 126–132 sq ft of flooring to be safe.
How do I calculate cost per square foot?
Multiply the square footage by the price per square foot. For 120 sq ft at $3.50/sq ft, the material cost is 120 × 3.50 = $420 before waste.
How do I figure square footage for an irregular room?
Split the room into rectangles, calculate each one's area (length × width), and add them together. For round or angled sections, use the circle or triangle formula.