Area of a Circle

Imagine slicing a circle into very thin pie wedges and rearranging them into something close to a rectangle. The “rectangle” has height r (the radius) and width πr (half the circumference). Its area is πr · r = πr².

So for any circle:

Doubling the radius multiplies the area by four, not two — radius enters the formula squared. Watch the readout as you drag the slider.