Free Online Area Calculator
An area calculator returns the surface area of common 2D shapes — rectangle, triangle, circle, trapezoid, ellipse, and regular polygons — from their dimensions.
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How to Use This Calculator
- Pick the shape from the dropdown selector.
- Type the dimensions the shape needs into the labelled inputs.
- Read the area and the formula used in the result panel.
What Is an Area Calculator?
Each common shape has a closed-form area formula. Rectangle = w × h. Triangle = ½ × b × h. Circle = π × r². Trapezoid = ½ × (a + b) × h, where a and b are the parallel sides. Ellipse = π × a × b, where a and b are the semi-axes. Regular polygon = ¼ × n × s² × cot(π/n), where n is the side count and s is the side length.
This page picks the right formula from a dropdown and asks for only the inputs that shape needs. Each result prints both the numeric area and the formula that produced it, so it doubles as a quick reference for homework or back-of-envelope checks.
Units are whatever you put in — feed inches and you get square inches, feed cm and you get square centimetres. Mixing units in one calculation will produce nonsense, so convert to a single unit first.
Frequently Asked Questions
What shapes are supported?
How do I find the area of an irregular shape?
What units can I use?
Published by the WeGotEveryTool team. We build and test every tool in-house and update pages when the underlying spec, formula, or recommendation changes.
Reviewed: May 2026. Disclaimer: this tool is provided as-is for general informational use. For decisions with material consequences (medical, legal, financial, security) verify results against a qualified professional source.
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