To find the diameter of a circle given its circumference, we can use the formula for the circumference:
\[ C = \pi d \]
where \(C\) is the circumference and \(d\) is the diameter. Given that the circumference \(C = 20\pi\), we can set up the equation:
\[ 20\pi = \pi d \]
To solve for \(d\), we can divide both sides by \(\pi\):
\[ 20 = d \]
Thus, the diameter of the circle is \(20\) units.