## Calculator

Enter the radius, diameter, circumference or area of a Circleto find the other three.The calculations are done "live":

## How come Remember?

To help you psychic think "Pie are Squared"(even though pies room usually round)

## Comparing a Circle to a Square

It is amazing to compare the area that a circle come a square:

A one has around 80% of the area the a similar-width square.

You are watching: Why is the area of a circle pi r 2

The actual value is (π/4) = 0.785398... = 78.5398...%

Why? due to the fact that the Square"s Area is w2and the Circle"s Area is (π/4) × w2

### Example: to compare a square come a one of width 3 m

Square"s Area = w2 = 32 = 9 m2

Estimate the Circle"s Area = 80% of Square"s Area = 80% of 9 = 7.2 m2

Circle"s True Area = (π/4) × D2 = (π/4) × 32 = 7.07 m2 (to 2 decimals)

The estimate of 7.2 m2 is not much off 7.07 m2

### Example: Max is structure a house. The very first step is to drill holes and also fill them with concrete.

The holes space 0.4 m wide and also 1 m deep, how much concrete need to Max order for each hole?

The holes space circular (in overcome section) since they space drilled out making use of an auger.

See more: One Troy Ounce 999 Fine Silver Liberty Head " Made In Us 1 Troy Ounce

The diameter is 0.4m, for this reason the Area is:

A = (π/4) × D2

A = (3.14159.../4) × 0.42

A = 0.7854... × 0.16

A = 0.126 m2 (to 3 decimals)

And the holes are 1 m deep, so:

Volume = 0.126 m2 × 1 m = 0.126 m3

So Max must order 0.126 cubic meter of concrete to to fill each hole.

Note: Max can have estimated the area by:

1. Calculating a square hole: 0.4 × 0.4 = 0.16 m22. Taking 80% of that (estimates a circle): 80% × 0.16 m2 = 0.128 m23. And the volume of a 1 m deep hole is: 0.128 m3

And something interesting for you:

See one Area by Lines

circle Circle Area by Sectors Geometry Index