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Area Calculator

Calculate area for 12 plane shapes, including rectangles, circles, polygons, sectors, ellipses, kites, and annuli.

  • shape area calculator
  • geometry area calculator
  • regular polygon area calculator
  • ellipse area calculator
  • sector area calculator

Choose the plane shape whose area you want to calculate.

Rectangle length.

Rectangle width.

Status: initial

Results

Awaiting calculation

Explore your result

Calculated area scale

See the selected shape's area on a consistent scale, then review the exact substitution in the result table.

Calculated area scale
240 square units
SmallCompactMediumLargeVery large

Use this result well

  1. 1Confirm the selected shape and required dimensions.
  2. 2Keep every entered dimension in the same unit.
  3. 3Review the formula and substitution shown with the result.

Use one length unit for every dimension; the resulting area uses that unit squared.

Geometry guide

Introduction

The Area Calculator finds the two-dimensional space inside 12 common plane shapes. Choose a shape and the form shows only the dimensions required for that formula. Each supported shape uses its own two-dimensional formula, and the result is expressed in square units based on the consistent length unit supplied.

When to use an area calculator

Use it for geometry practice, floor and garden planning, material estimates, diagrams, and quick comparisons. Enter every dimension in the same length unit so the answer is expressed in that unit squared. For material purchasing, calculate the geometric area first and then add a project-specific allowance for cuts, overlap, defects, or waste.

How area is calculated

Each shape has its own formula. The calculator substitutes your dimensions into the selected formula, keeps full precision during calculation, and displays the final area to four decimal places when needed. A circle requires a radius, while triangle and trapezoid formulas require perpendicular height rather than a sloping side length.

Variable explanations

Understand what each input and result means before calculating.

Shape

Controls which formula and dimension fields are used.

Length, width, and side

Straight-edge dimensions used by quadrilaterals and regular polygons.

Radius

Distance from a circle's centre to its edge; it is half the diameter.

Base and height

Height must be perpendicular to the selected base.

Diagonals

Corner-to-corner lengths used for rhombus and kite area.

Ellipse axes

Semi-major and semi-minor axes are half the full ellipse diameters.

Central angle

The sector's angle in degrees, from greater than 0° through 360°.

Inner and outer radii

The inner radius must be smaller than the outer radius for an annulus.

Reviewed by the Calculator.org.in Editorial Team

Formula behavior, validation cases, explanatory examples, and cited sources are checked before publication. This review supports educational accuracy and is not a substitute for qualified professional advice.

Last reviewed: 2026-08-23

Review process

Formula guide

See the calculation logic, variable definitions, and practical meaning.

Rectangle and square

Rectangle: A = l × w; Square: A = s²

  • l is length.
  • w is width.
  • s is side length.

Multiply perpendicular dimensions; for a square both dimensions are equal.

Circle, sector, and annulus

Circle: A = πr²; Sector: A = θ/360 × πr²; Annulus: A = π(R² − r²)

  • r is radius.
  • R is outer radius.
  • θ is the central angle in degrees.

A sector is a fraction of a circle, while an annulus subtracts the inner circle.

Triangle and parallelogram

Triangle: A = bh/2; Parallelogram: A = bh

  • b is base.
  • h is perpendicular height.

A triangle with the same base and height has half the parallelogram's area.

Trapezoid

A = (b₁ + b₂)h/2

  • b₁ and b₂ are the parallel sides.
  • h is perpendicular height.

Average the two parallel sides, then multiply by their perpendicular separation.

Rhombus and kite

A = d₁d₂/2

  • d₁ and d₂ are the diagonals.

Multiply the diagonals and divide by two.

Ellipse

A = πab

  • a is the semi-major axis.
  • b is the semi-minor axis.

The axes are half of the ellipse's full diameters.

Regular polygon

A = ns² / (4 tan(π/n))

  • n is the number of sides.
  • s is the common side length.

This formula applies when every side and interior angle are equal.

Worked examples

Follow realistic inputs through the calculation step by step.

1

Worked example

Rectangle

  1. 1Choose Rectangle.
  2. 2Enter length 5 and width 4.
  3. 3The area is 20 square units.
2

Worked example

Regular hexagon

  1. 1Choose Regular polygon.
  2. 2Enter 6 sides and side length 4.
  3. 3The area is approximately 41.5692 square units.
3

Worked example

Quarter-circle sector

  1. 1Choose Circular sector.
  2. 2Enter radius 6 and angle 90°.
  3. 3The area is approximately 28.2743 square units.
4

Worked example

Annulus

  1. 1Choose Annulus.
  2. 2Enter outer radius 5 and inner radius 3.
  3. 3The area is approximately 50.2655 square units.
5

Worked example

Find the area of a circle

  1. 1Choose circle and enter a radius of 3.
  2. 2Square the radius and multiply by π.
  3. 3The area is approximately 28.2743 square units.
6

Worked example

Find the area of a trapezoid

  1. 1Choose trapezoid, enter bases 8 and 12, and height 6.
  2. 2Average the parallel bases: (8 + 12) ÷ 2 = 10.
  3. 3Multiply by height to obtain 60 square units.

Common mistakes

Avoid these common input and interpretation errors.

Mixing units

Convert all dimensions to the same length unit before calculating.

Using diameter as radius

Divide the diameter by two before entering a circle or sector radius.

Using slanted height

Triangle, trapezoid, and parallelogram formulas require perpendicular height.

Entering full ellipse axes

The ellipse fields expect half of each full diameter.

Using an irregular polygon

The regular-polygon formula assumes equal sides and equal angles.

Reversing annulus radii

The inner radius must be smaller than the outer radius.

Frequently asked questions

Quick answers to the questions users ask most often.

Which shapes are supported?
Rectangle, square, circle, triangle, trapezoid, parallelogram, rhombus, kite, ellipse, regular polygon, circular sector, and annulus.
Can I use centimetres, metres, feet, or inches?
Yes. Use one consistent length unit for all inputs; the result is in the corresponding square unit.
Why do the inputs change when I choose a shape?
Only dimensions used by the selected shape's formula are shown, reducing irrelevant inputs and mistakes.
What is perpendicular height?
It is the shortest distance from a base to the opposite side or vertex, measured at 90 degrees to the base.
Can this calculate an irregular polygon?
Not directly. Split an irregular polygon into supported shapes, calculate each area, then add or subtract them.
How do I use a diameter?
Divide the diameter by two and enter the result as radius.
What is an annulus?
An annulus is a ring-shaped region between two circles that share the same centre.
Can a sector be a full circle?
Yes. Enter 360 degrees and the sector formula produces the same area as a circle with that radius.
How many sides can a regular polygon have?
This calculator accepts whole numbers from 3 through 100.
Why is the answer in square units?
Area measures two-dimensional space, so its unit is the entered length unit multiplied by itself.
What is the difference between area and perimeter?
Area measures the surface enclosed by a boundary in square units; perimeter measures the distance around that boundary in linear units.
Can I add areas of multiple shapes?
Yes. Divide an irregular region into supported shapes, calculate each area using one common unit, then add non-overlapping parts and subtract cut-outs.
Should I include a waste allowance?
The geometric result does not include waste. Add a percentage appropriate to the material and installation pattern after calculating the base area.

References

Sources used to support the calculator guidance.

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Version history

A transparent record of calculator content updates.

Updated 2026-08-23
  • 2.0.0 · 2026-08-23

    Expanded from 4 to 12 shapes, added shape-specific inputs, calculation steps, validation, formulas, examples, and unique page content.

  • 1.0.0 · 2026-08-03

    Initial rectangle, circle, triangle, and trapezoid calculator.