Free Area Calculator for 2D Shapes, With Steps
Choose a rectangle, square, triangle, circle, trapezoid, parallelogram, ellipse or regular polygon. Enter dimensions in one unit to see the formula, substitution and area, plus conversion to square metres. Use the three-side triangle mode when you do not know the height.
Enter your values or load an example to see the answer and worked steps. Calculations run in your browser.
Select the shape before entering dimensions
A rectangle needs length and width; a square needs one side. A triangle and parallelogram use a base and perpendicular height. A trapezoid uses both parallel sides and the perpendicular distance between them. The tool changes its fields to match your selection.
Radius, diameter and semi-axis are different measurements
The circle input is radius, so divide a supplied diameter by two first. An ellipse uses two semi-axes, each half a full axis length. Entering a diameter where a radius is requested multiplies the circle area by four.
Work a triangle in two ways
A triangle with sides 3, 4 and 5 cm has semiperimeter 6 cm. Heron’s formula gives √[6 × 3 × 2 × 1] = 6 cm². Using the perpendicular legs as base and height gives 3 × 4 / 2 = 6 cm². The three-side mode rejects lengths that do not form a triangle.
Regular polygons require equal sides and angles
For n equal sides of length a, area is na²/[4 tan(π/n)]. This formula assumes a regular polygon and cannot solve an arbitrary outline from one side length. The angle inside the tangent is in radians.
Square the conversion factor
A rectangle measuring 8 cm by 5 cm has area 40 cm². Since 1 cm = 0.01 m, the converted area is 40 × 0.01² = 0.004 m². Converting only once as if area were a length gives the wrong unit and number.
Related free tools
Frequently Asked Questions
Can I enter a mixture of centimetres and metres?
No. Convert all lengths to the selected common unit first. The result also shows the equivalent area in square metres.
Which triangle height should I enter?
The perpendicular distance from the opposite vertex to the base line, not a sloping side. If only three sides are known, use the Heron mode.
Can this calculate an irregular polygon?
Not from one side length. Break the outline into supported shapes or use a coordinate-based method. The polygon mode here is for regular polygons only.
Is area the same as surface area or volume?
No. This tool calculates flat two-dimensional area. Use the volume calculator for supported three-dimensional solids.
Continue in the app
Use Geometry AI - Math Solver for the full guided result after this quick check.
