Free Area Calculator for Rectangles, Circles, Triangles, Trapezoids, Ellipses, and Regular Polygons

Choose a common 2D shape, enter its dimensions, and calculate area with the exact formula, related perimeter when available, and a simple visual reference.

Browser-basedNo sign-upPrivate local historyStep-by-step

Interactive calculator

Shape

Dimension A

Dimension B

Dimension C / angle / sides

Area—

Perimeter / arc—

Shape—

Choose a shape and enter dimensions.

How to use it

Choose the 2D shape you want to calculate.
Enter the dimensions requested for that shape.
Keep all linear inputs in the same unit.
Calculate and review the formula substitution.
Report the final area in squared units and perimeter in linear units.

What this calculator includes

1. RectangleArea and perimeter from length and width.

2. SquareArea and perimeter from one side.

3. CircleArea and circumference from radius.

4. TriangleArea from base and perpendicular height.

5. TrapezoidArea from parallel bases and height.

6. ParallelogramArea from base and height.

7. EllipseArea from semi-major and semi-minor axes.

8. SectorArea and arc from radius and angle.

9. Regular polygonArea from side length and side count.

10. Unit-neutralUse any consistent linear unit.

11. Formula stepsShows the selected geometry formula.

12. Local historySave recent shape calculations.

Result checklist

0 / 5 complete

Inputs use the intended units or interpretation.The formula mode matches the problem.The result magnitude is reasonable.I reviewed the shown calculation steps.I will round only at the final step.

Local calculation history

Formula and reference table

Shape	Area formula	Main inputs
Rectangle	lw	length, width
Circle	πr²	radius
Triangle	bh/2	base, height
Trapezoid	(a+b)h/2	parallel bases, height
Ellipse	πab	semi-axes
Regular polygon	ns²/[4tan(π/n)]	side count, side

Quick knowledge check

What happens to the area of a square if its side length doubles?

Related calculators

Circle Calculator Triangle Area Right Triangle

Frequently asked questions

What units does the area calculator use?

It is unit-neutral. If lengths are in meters, the area is in square meters; if lengths are in feet, the area is in square feet.

Can I calculate irregular shapes?

Not directly. Split an irregular shape into supported simple shapes and add or subtract their areas.

What is the difference between area and perimeter?

Area measures the surface enclosed by a shape, while perimeter measures the length around its boundary.

Does a sector use degrees or radians?

Enter degrees; the calculator converts the angle internally before computing area and arc length.

Scope and accuracy

This page covers ideal planar shapes. Real-world measurements, curved-surface areas, map projections, and irregular boundaries can require additional methods or measurement uncertainty.