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Area Calculator

Calculate the area of various geometric shapes using precise mathematical formulas.

Rectangle Calculator

Area

What Is an Area Calculator?

An Area Calculator helps you find the amount of flat space inside a two-dimensional shape. It is useful for geometry, construction, flooring, painting, land measurement, design, and everyday measurement problems.

Area is always a square measurement. If the side lengths are in feet, the answer is in square feet. If the side lengths are in meters, the answer is in square meters.

Meaning

What Is Area?

Area measures how much surface a shape covers. It does not measure distance around the shape; that is perimeter. It does not measure 3D space; that is volume.

Simple rectangle example

A=length×widthA=\text{length}\times\text{width}

Example: a rectangle that is 10 feet long and 5 feet wide has an area of 50 ft^2.

Calculator Uses

What This Area Calculator Can Do

The calculator covers the most common 2D shapes and shows the math used for the final area.

Multiple shapes
Calculate area for rectangles, triangles, trapezoids, circles, sectors, ellipses, and parallelograms.
Formula steps
Review the formula and substituted values so the answer is easier to verify.
Square unit result
Use the same input unit for every measurement, then read the answer in square units.
Geometry checks
For triangle side lengths, the calculator checks that the sides can form a real triangle.

The Math

Common Area Formulas

Use the formula that matches the selected shape and the measurements you have.

ShapeFormulaHow to read it
RectangleA=l×wA=l\times wLength times width.
TriangleA=12bhA=\frac{1}{2}bhBase times perpendicular height, divided by 2.
Triangle with 3 sidesA=s(s−a)(s−b)(s−c)A=\sqrt{s(s-a)(s-b)(s-c)}Heron's formula, where s is the semi-perimeter.
TrapezoidA=b1+b22×hA=\frac{b_1+b_2}{2}\times hAverage of the two parallel bases times height.
CircleA=πr2A=\pi r^2Radius squared times pi.
SectorA=θ360×πr2A=\frac{\theta}{360}\times\pi r^2Circle area scaled by the central angle in degrees.
EllipseA=πabA=\pi abSemi-major axis times semi-minor axis times pi.
ParallelogramA=bhA=bhBase times perpendicular height.

Heron's formula semi-perimeter

s=a+b+c2s=\frac{a+b+c}{2}

For a triangle with three known side lengths, first calculate s, then use it inside Heron's area formula.

How to Use

How to Use This Area Calculator

Choose the shape, enter the required values, calculate, then review the result and steps.

  1. 1

    Select a shape

    Choose rectangle, triangle, trapezoid, circle, sector, ellipse, or parallelogram.

  2. 2

    Enter measurements

    Use the same unit for all values, such as all feet or all meters.

  3. 3

    Calculate area

    Click Calculate Area to see the square-unit result.

  4. 4

    Check the steps

    Use the formula breakdown to confirm the answer and catch unit mistakes.

Units

Why Square Units Matter

Area multiplies two dimensions, so the unit is squared.

Input unitArea unit
Input in inchesAnswer is square inches, written as in^2
Input in feetAnswer is square feet, written as ft^2
Input in centimetersAnswer is square centimeters, written as cm^2
Input in metersAnswer is square meters, written as m^2
If one measurement is in meters and another is in centimeters, convert them first. Mixed units create misleading area results.

Common Mistakes

Area Calculation Mistakes to Avoid

Most wrong answers come from using the wrong measurement, the wrong unit, or the wrong version of a formula.

Using slanted side as height
For triangles, trapezoids, and parallelograms, height means the perpendicular distance from the base.
Mixing units
Convert all measurements to the same unit before calculating. Do not multiply feet by inches or meters by centimeters.
Using diameter as radius
Circle and sector formulas use radius. If you have diameter, divide it by 2 first.
Writing linear units
Area is measured in square units, so a result should be written as ft^2, m^2, cm^2, or another square unit.

Use Cases

Where Area Calculations Are Used

Area is a practical measurement used far beyond math class.

Use caseWhy area matters
Flooring and tileEstimate how much floor area must be covered.
Painting and wall workFind wall or ceiling area before buying material.
Land measurementEstimate lot, garden, field, or landscaping area.
Design and constructionSize rooms, panels, surfaces, and layouts.
School geometryPractice formulas and check step-by-step answers.
Geometry Help

Frequently Asked Questions

An area calculator finds the amount of flat space inside a 2D shape, such as a rectangle, triangle, circle, trapezoid, ellipse, sector, or parallelogram.

Rectangle area is length times width.

Triangle area is one-half times base times height. If you know all three side lengths, Heron's formula can also be used.

Circle area is pi times radius squared.

Trapezoid area is the average of the two parallel bases times height.

Ellipse area is pi times a times b, where a and b are the semi-major and semi-minor axes.

Area is measured in square units, such as square feet, square meters, square inches, or square centimeters.

Not always. For triangles, trapezoids, and parallelograms, height is the perpendicular distance from the base, not the slanted side.

Divide the diameter by 2 to get the radius, then use the circle area formula.

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