Area Calculator… Your Ultimate Guide

Which Area Calculator Should You Use and Why?

This Ultimate Guide seeks to answer that question and provide a compendium of the web’s top Area Calculators and when to use them.

Our compendium is organised by use-case, i.e. what shape you need to find the area of, then listed in order of the most commonly used area calculators.

Find the Area of a Circle

Find the Area of a Triangle

Find the Area of a Trapezoid

Find the Area of a Quadrilateral

Find the Area of a Parallelogram

Find the Area of Irregular Shapes

Area of a Circle

To find the area of a perfect circle you’ll need one of three things:

The Radius

A straight line extending from the circles center to its edge.

The Diameter

A straight line passing from side to side through the circles centre.

The Circumference

The linear distance of a circle’s edge.

If you have at least one of those measurements head on over to:

Maths is fun

Area of a Circle

A super simple interface that resolves a circles area when either radius, diameter, or circumference is entered. It’s a great resource for regular polygon shapes when you know some of the dimensions.

Keisan Online Calculator

Area of a Circle Calculator

If you have the circles radius or diameter this area calculator will provide both area and circumference of a circle. Lacking circle circumference as an input reduces its utility a little but its just as accurate as Maths is Fun.

Calculator Soup

Circle Calculator

A little less intuitive, but similar to Maths is Fun, Calculator Soup finds a Circles Area when either Radius, Diameter, or Circumference is entered. 


Area of a Circle you draw

SketchAndCalc offers a different approach. If you only have the circles diameter, or just an idea of the space the circle needs to occupy inside an imported image or map, SketchAndCalc might be the best option. Once the scale is set, the act of drawing the circle at any given scale (nanometers to miles) will resolve the area results.

Area of a Triangle

How to find the area of a triangle depends on what you know about the triangle.

If you have the triangles base and height simply multiply those two together and divide by 2 and you have your area (Area = base x height / 2)

If you know the lengths of the triangles sides you’ll need to use Heron’s formula or tap the lengths onto:

Maths is fun

Area of a Triangle from Sides (Heron’s formula)

Whilst ‘Maths is fun’ isn’t the only triangle area calculator using side lengths (Heron’s formula), it made our list because it’s arguably the most intuitive, updating the area and angles as the lengths of the sides change.

If you know the angle and lengths of two sides head on over to:

Open Math Reference

Area of a triangle – “side angle side” (SAS) method

This triangle area calculator from Open Math Reference provides the math formula in the top left which updates as you make adjustments to both line lengths and the angle. This is similar to the way SketchAndCalc works abet without displaying the length of the third side and remaining angles.

If you need to calculate the area of a triangle in an image or represented on a map try:


Draw triangle over a map or image

Whether you’re starting with a blank grid, image, or a map, draw out your triangle then move the vertices into position to represent the line lengths and angles you need. You can also tap in precise line lengths and display the angles when a vertex is selected.

Collect the area of a triangle along with its perimeter in the bottom right corner.

Area of a Trapezoid

A trapezoid is a four-sided shape with at least one set of parallel sides, as opposed to a quadrilateral that is any four-sided shape.

If you want to find the area of a trapezoid you’ll need two things:

The lengths of the two parallel lines (running horizontally).

The height of the shape (vertically).

If you have both of those head on over to:

Keisan Online Calculator

Area of a trapezoid Calculator

Again, the trapezoid calculator at Keisan Online Calculator isn’t the only one out there but we like it’s clean, simple inputs.

Area of a Quadrilateral

A quadrilateral is any four sided shape regardless of angles or line lengths.

To calculate the area of a quadrilateral you will need the following six things:

The lengths of all four sides.

Two of the four angles.

If you have all that, go to:

Keisan Online Calculator

Area of a Quadrilateral Calculator

Finding the area of a quadrilateral requires a lot of inputs. If you don’t know all four lengths and both angles but you have an idea of what the shape looks like, or you have an image containing the shape you can draw it out using:


Area of Irregular Shapes

Prior to drawing your quadrilaterals area, import its image, and set the drawing scale by drawing along a known length (as prompted during the image import process).

Area of a Parallelogram

A parallelogram is any shape with opposing sides that are equal in length, run parallel with each other, and have opposite angles that are equal in measure.

So by definition, Squares, Rectangles and Rhombuses are all Parallelograms.

Find the area of a parallelogram by multiplying the base and height together, or head on over to:


Parallelogram Area Calculator

If you have the side lengths and the parallelogram’s angle change the ‘Given’ value to: sides + angle between

Parallelogram Sides and Angle Area Calculator

If you only know the line lengths of your parallelogram and haven’t any of the angles you’ll need to draw out the shape with:


Parallelogram Area Calculator

Using SketchAndCalc’s ‘Constrained Line Drawing Tool’ it’s possible to draw a perfect parallelogram. Adjust the line lengths manually by moving the vertices, or simply select a line length label and enter the desired length.

Area of Irregular Shapes

Measure any irregular area over maps, images or plans with SketchAndCalc.


Irregular Area Calculator

Set the scale of an image with a known length, or in the case of area of maps just search the address and start drawing the perimeter of the shape or shapes you wish to calculate.

We hope this guide was helpful and saved you some time. If there are regular or irregular polygon area calculators that you would like to see included do let us know.

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