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Area Calculator

Pick a shape, enter its dimensions, and get the area and perimeter at once.

Shape

Dimensions

Enter every dimension in the same unit. Everything runs in your browser. Nothing is uploaded.

Unit

Decimal places

Result

Area
40 sq m
l × w
Perimeter
26 m
In m

Everything is calculated in your browser. Nothing is uploaded.

How to calculate the area of a shape

  1. Choose a shape

    Select the shape you are measuring, from rectangle and square to triangle, circle, trapezoid, parallelogram, or ellipse.

  2. Enter its dimensions

    Type the side lengths, radius, or height the shape needs, using the same single unit for all of them.

  3. Pick a unit

    Choose the unit label so the area reads in square units and the perimeter in plain units.

  4. Read and copy

    The area and perimeter update as you type and can be copied as a short summary.

Why use this tool

Seven shapes in one tool

Rectangle, square, triangle, circle, trapezoid, parallelogram, and ellipse each get the right inputs and the correct formula.

Area and perimeter together

Every shape returns its area and, where it is defined, its perimeter or circumference in the same unit.

Catches impossible triangles

Three side lengths that cannot close into a triangle are flagged instead of returning a wrong or blank area.

Unit label you choose

Set the unit once and results read as square units for area and plain units for length, from millimetres to miles.

Adjustable precision

Show 2, 4, or 6 decimal places to keep answers short or exact.

Runs entirely in your browser

Every calculation happens on your device. Nothing you enter is uploaded.

About this tool

This area calculator works out the area of the shape you choose and, wherever a perimeter is defined, the distance around it too. Pick from a rectangle, square, triangle, circle, trapezoid, parallelogram, or ellipse, and the inputs change to match: two sides for a rectangle, a single side for a square, three sides for a triangle, a radius for a circle, and so on. Each shape uses its standard formula, so the numbers match what you would get by hand.

Enter every dimension in the same unit and the results follow that unit: area comes back in square units and perimeter in plain units, with a label from millimetres up to miles that you set yourself. A triangle is solved from its three sides using Heron's formula, and any three lengths that cannot actually close into a triangle are rejected rather than returning a misleading answer. The ellipse perimeter uses a well known close approximation, since an ellipse has no exact elementary circumference. If you need to move a result between units of length or area afterwards, the unit converter handles that.

Zero and negative dimensions are caught with a clear message instead of a broken result, and everything recalculates the moment you type, with no button to press. For a deeper look at one shape try the circle calculator or the triangle calculator, which solve for extra measurements from what you already know.

Frequently asked questions

How do I calculate the area of a shape here?
Choose the shape, type its dimensions in a single unit, and the area appears at once using that shape's standard formula. The perimeter or circumference is shown alongside it whenever the shape defines one.
Which shapes and dimensions are supported?
Rectangle (length and width), square (side), triangle (three sides), circle (radius), trapezoid (two parallel sides, two legs, and height), parallelogram (base, side, and height), and ellipse (two semi-axes).
How does it handle an impossible triangle?
A triangle only exists when each side is shorter than the sum of the other two. If the three lengths you enter break that rule, the calculator flags them instead of showing a wrong area.
What units does it use?
It is unit-agnostic. Enter every dimension in the same unit and pick a label from millimetres to miles. Area is reported in square units and perimeter in the plain unit.
Why is the ellipse perimeter marked as approximate?
An ellipse has no exact perimeter formula in elementary terms, so its circumference uses a very accurate standard approximation. The area, which is exact, is not affected.
Is my data uploaded anywhere?
No. Everything runs in your browser; nothing is sent to a server.

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