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