Area and Circumference of a Circle

Area – number of square units enclosed in the circle

A=\pi r^{2}

Circumference – distance around the circle

C=\pi\times d


\pi\ (Pi)=3.14\ (constant)






diameter = 2â‹…radius







If a circle has a circumference of 15.7 cm, what is the area?

C=\pi\times d

\frac{C}{\pi}=\frac{\pi\times d}{\pi}


d=\frac{15.7\ cm}{3.15}

d=5\ cm

d=2\times r


r=\frac{5\ cm}{2}

r=2.5\ cm

A=\pi\times r^{2}

A=(3.14)(2.5\ cm)^{2}

A=19.625\ cm^{2}