The circumference of a circle = \(\pi d\) or \(2\pi r\). Look at the sector of the circle shown below. To calculate the length of the arc, we need to know what fraction of the circle is shown.

text{arc length} = \frac{\theta}{360}\times \pi d\) It's important to learn the formulae above, as they will not appear on the formula sheet ... of a circle with a radius of 15cm.