Area Calculator
Calculate the area of rectangles, circles, triangles, and more — instantly.
What is an Area Calculator?
An Area Calculator is a geometry tool that measures the area of a shape, which is the amount of flat space inside its boundaries. Area is used in many real-world tasks—like estimating how much paint you need for a wall, how much flooring or carpet to buy, how large a garden bed is, or how much material is required to cover a surface.
Different shapes have different area formulas. For example, rectangles use length × width, triangles use (base × height) ÷ 2, and circles use πr². An area calculator lets you choose the shape, enter the required dimensions, and instantly compute the area—without worrying about formula mistakes.
Area is always expressed in square units, such as square inches (in²), square feet (ft²), square meters (m²), or square centimeters (cm²). If your inputs are in feet, your output will be in square feet; if your inputs are in meters, your output will be in square meters.
Supported Shapes in This Calculator:
- Rectangle -- length and width
- Circle -- radius
- Triangle -- base and height
- Square -- side length
How to Use This Area Calculator
- Select the shape -- choose from Rectangle, Circle, Triangle, or Square using the tabs above
- Enter the required measurements -- such as length/width, radius, base/height, or side length
- Choose units if applicable -- use consistent units for all inputs (in, ft, cm, m)
- Click "Calculate" -- to compute the area
- Review the result -- confirm it's displayed in square units
Tips:
- Use consistent units for all inputs (don't mix inches and feet unless you convert first)
- If the calculator asks for radius, don't enter the diameter by mistake (diameter = 2 × radius)
- If you're estimating materials, consider adding a small extra percentage for waste (cutting, trimming, mistakes)
Area Formulas
Below are the most common area formulas used in geometry.
Rectangle
A = l × w
Where l = length and w = width
Square
A = s²
Where s = side length
Triangle
A = (b × h) ÷ 2
Where b = base and h = height
Circle
A = πr²
Where r = radius and π ≈ 3.14159
Parallelogram
A = b × h
Where b = base and h = perpendicular height
Trapezoid
A = ((a + b) ÷ 2) × h
Where a and b are the parallel sides, h is the height
Ellipse
A = πab
Where a and b are the semi-major and semi-minor axes
Example Calculations
Example 1: Rectangle Area
Length: 12 ft, Width: 8 ft
Calculation: A = 12 × 8 = 96
Result: 96 ft²
Example 2: Triangle Area
Base: 10 cm, Height: 6 cm
Calculation: A = (10 × 6) ÷ 2 = 60 ÷ 2 = 30
Result: 30 cm²
Example 3: Circle Area
Radius: 7 m
Calculation: A = π × 7² = π × 49 ≈ 153.94
Result: Area ≈ 153.94 m²
Example 4: Trapezoid Area
Parallel sides: a = 6 in, b = 10 in, Height: 4 in
Calculation: A = ((6 + 10) ÷ 2) × 4 = (16 ÷ 2) × 4 = 8 × 4 = 32
Result: 32 in²
Frequently Asked Questions
What is area measured in?
Area is measured in square units, such as in², ft², cm², or m². The "square" part comes from multiplying two lengths (like length × width).
What's the difference between area and perimeter?
Area is the space inside a shape. Perimeter is the distance around the outside of a shape. Area is in square units; perimeter is in regular units.
How do I know if I should use radius or diameter for a circle?
The area formula uses radius (r). If you have the diameter (d), convert it by using r = d ÷ 2.
Why do I get different results when I change units?
The number changes because the unit size changes (1 ft is bigger than 1 in). If you convert inputs correctly, the area will be consistent. For example, 1 ft² equals 144 in².
How do I estimate material needs using area?
Calculate the area of the surface, then compare it to the coverage of your material (paint coverage per gallon, tile area per box, etc.). It's common to add 5–15% extra for waste or cuts.
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What Is Area?
Area is the measure of the two-dimensional space enclosed within a shape, expressed in square units such as square feet (ft²), square meters (m²), or square centimeters (cm²). Whether you're figuring out how much flooring to buy for a living room, how much paint to cover a wall, or how much sod to order for a yard, area is the number you need. It shows up constantly in home improvement, landscaping, construction, and everyday geometry.
Every shape has its own area formula, and using the wrong one leads to costly mistakes — too little material ordered, or too much wasted. A rectangle and a triangle with the same base and height have very different areas. That's why this calculator covers eight of the most common shapes, so you can always choose the right formula for the job. Enter your dimensions, pick your shape, and get an accurate result in seconds.
How to Use This Calculator
- 1Select the shape you want to calculate from the dropdown menu — rectangle, square, circle, triangle, trapezoid, ellipse, parallelogram, or regular hexagon.
- 2Enter the required dimensions for your chosen shape (e.g., length and width for a rectangle, or radius for a circle).
- 3Click the Calculate button to compute the area instantly.
- 4Read the result — displayed with the correct square unit label (ft², m², cm², etc.) matching your input unit.
Area Formulas for Every Shape
Rectangle: A = length × width
Square: A = side²
Circle: A = π × radius² (π ≈ 3.14159)
Triangle: A = ½ × base × height
Trapezoid: A = ½ × (a + b) × height
Ellipse: A = π × a × b
Parallelogram: A = base × height
Regular hexagon: A = (3√3 / 2) × side²All dimensions must be in the same unit before calculating. The result unit is the square of the input unit — for example, if you enter feet, the area is in ft²; if you enter centimeters, the area is in cm².
Worked Examples
Living Room Flooring — Rectangle
You have a living room that measures 15 ft × 20 ft. Using A = length × width: A = 15 × 20 = 300 ft². You need 300 ft² of flooring. Most contractors recommend adding 10% for waste and cuts, so order 300 × 1.10 = 330 ft² to be safe.
Circular Garden Bed — Circle
You're planning a circular garden with a radius of 4 meters. Using A = π × r²: A = 3.14159 × 4² = 3.14159 × 16 = 50.27 m². You'll need enough mulch or soil to cover just over 50 square meters.
Triangular Land Plot — Triangle
A triangular section of your yard has a base of 30 ft and a height of 25 ft. Using A = ½ × base × height: A = ½ × 30 × 25 = 375 ft². That's the amount of grass seed or ground cover you'd need to fill the plot.