Area CalculatorFree online math calculator — instant results, no sign-up
Area of common 2D shapes.
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About the Area Calculator
This calculator computes the surface area of six standard two-dimensional geometric figures: rectangles, triangles, circles, trapezoids, ellipses, and parallelograms. It is designed for students, educators, designers, and tradespeople who need quick, precise geometric calculations. Select the target shape and input the corresponding linear measurements to find the total enclosed area.
- Shape
- The geometric figure to evaluate: Rectangle, Triangle, Circle, Trapezoid, Ellipse, or Parallelogram.
- Dimension a (length/base/radius)
- Primary linear measure: length for a rectangle, base for a triangle/parallelogram/trapezoid bottom, or radius/semi-major axis for a circle/ellipse. Must be positive.
- Dimension b (width/height)
- Secondary linear measure: width for a rectangle, perpendicular height for a triangle/parallelogram/trapezoid, or semi-minor axis for an ellipse. Unused for circles.
- Dimension c (trapezoid top)
- The parallel top base length of a trapezoid. Only utilized when Trapezoid is selected.
Formula and method
Rectangle: Area = a × b Triangle: Area = (a × b) / 2 Circle: Area = π × a² Trapezoid: Area = ((a + c) / 2) × b Ellipse: Area = π × a × b Parallelogram: Area = a × b
- aLength, bottom base, circle radius, or ellipse semi-major axis
- bWidth, perpendicular height, or ellipse semi-minor axis
- cTop base length of a trapezoid
- πMathematical constant pi (~3.141592653589793)
The tool reads the selected shape and evaluates its corresponding area equation using the provided dimensions. Standard mathematical pi (Math.PI) is used for circular and elliptical shapes. The final area is displayed rounded to up to 6 decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- ShapeRectangle
- Dimension a (length/base/radius)5
- Dimension b (width/height)3
- Dimension c (trapezoid top)2
Results
- Area15
How to use the Area Calculator
- 1Choose the target 2D shape from the dropdown menu.
- 2Enter dimension a representing the base, length, or radius.
- 3Enter dimension b representing the height, width, or secondary axis (if applicable to the shape).
- 4Enter dimension c for the opposite parallel edge if calculating a trapezoid, then view the computed area.
Reading your result
The result represents the total two-dimensional space enclosed by the shape's boundary. The output is in square units corresponding to the input linear units (for instance, inputting inches yields square inches, and meters yields square meters). Ensure all input dimensions share the exact same measurement unit.
Limitations
The calculator assumes regular planar Euclidean geometry and requires perpendicular heights rather than slant heights for triangles, parallelograms, and trapezoids. It does not convert between different measurement units automatically nor evaluate irregular polygons.
Common questions
What unit of measurement should I enter?+
You can use any linear unit (such as inches, feet, centimeters, or meters), but all dimensions must use the same unit. The calculated area will be in corresponding square units.
Why does a parallelogram use the same formula as a rectangle?+
Both calculate area as base multiplied by height. For a parallelogram, dimension b must be the perpendicular vertical height between the parallel bases, not the slant side length.
Which inputs are required for a circle?+
Only Dimension a is used for a circle, where it represents the radius (r). Dimensions b and c are ignored by the circle calculation.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.