Free Area Calculator Online
Calculate the area of any common shape — rectangles, circles, triangles, trapezoids, ellipses, and more. Just pick a shape, enter the dimensions, and this free area calculator gives you the result with the formula shown.
Enter the radius of the circle.
Circle Area
A = πr²
Area Formulas for Common Shapes
Every shape has its own area formula. The area calculator applies the correct one automatically, but knowing the math helps you verify results and estimate on the fly.
Rectangle
A = length x width
The most common area calculation. A 12 ft x 15 ft room = 180 sq ft. Works for any rectangle or square. For a square, both dimensions are equal, so A = side².
Circle
A = pi x r²
A circular garden with a 4-meter radius covers about 50.27 m². Remember that doubling the radius quadruples the area — a common source of underestimation.
Triangle
A = 1/2 x base x height
The height must be perpendicular to the base. A triangle with base 10 and height 6 has area 30. If you only know the three sides, use Heron's formula instead.
Trapezoid
A = 1/2 x (a + b) x h
Where a and b are the two parallel sides and h is the height between them. A trapezoid with bases 8 and 12, height 5 gives area = 50.
Worked Examples
Related Math Tools
Why Use This Free Area Calculator?
- Supports 8+ shape types
- Shows the formula used
- Instant live results
- Works on phone or desktop
- Always free, no sign-up
What People Use an Area Calculator For
Home Improvement
Flooring, painting, tiling, and carpet all start with one question: how many square feet? Measure the room, plug it into the area calculator, and you know exactly how much material to buy. Over-ordering wastes money; under-ordering wastes time.
Landscaping & Gardening
Sod, seed, mulch, and gravel are sold by the square foot or square yard. A lawn area calculator tells you exactly how much to order. For an irregularly shaped yard, break it into rectangles and triangles and add up the pieces.
School & College
Geometry homework, physics problems, and engineering coursework all involve area calculations. Use the area calculator to verify your manual work, or to quickly handle the computation steps in a larger problem.
Area Calculator Tips
Accurate results from the area calculator depend on accurate inputs. These tips help avoid the most common errors.
Use Consistent Units
If your length is in feet, the width must also be in feet. Mixing feet and inches is the number-one source of errors. Convert everything to the same unit before entering it into the area calculator.
Radius vs. Diameter
The circle area formula uses the radius (half the diameter). If you measure across the whole circle and get 10 feet, the radius is 5 feet. Using 10 instead of 5 gives you four times the correct area.
Height Means Perpendicular Height
For triangles and trapezoids, the height is the perpendicular distance between the base and the opposite side (or vertex). Measuring along a slanted side gives a larger number and an incorrect area.
Frequently Asked Questions
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