Circle Formulas, Circumference & Area

Formula

A special type of equation that shows the relationship between different variables.

Circumference of a Circle is the amount of linear units it takes to go around the circle . Similar to Perimeter

C = πd

C = 2πr

Circumference can be found if you know the radius

Diameter is the line segment that has endpoints on the circumference and goes thru the center point of the circle

D = 2r

In terms of pi

In terms of pi means to leave pi in you answer instead of multiplying by it.

Diameter

The distance across the circle through the center

Circumference

The distance all the way around a circle, like perimeter for polygons.

Radius

The distance from the center of a circle to any point on the circle

Area

The number of square units needed to cover a given surface

Exponent (square)

The number that indicates how many times the base is used as a factor

Pi (ratio)

The ratio of a circle's circumference to its diameter (3.14 or 22/7)

Semi-Circle

half of a circle; 180 degree arc

radius is 1/2 of the diameter, it's endpoins are the center of the circle and a point on the circumference

r = d/2 .