Welcome to the forum Jack.
As Guy has indicated, it is not a difficult calculation, you just need to Google
the reference material. You could do this yourself, but wherever you buy the prop will do the maths for you.
These calcuations are only a starting point. In practice, the prop may be a little under or over pitched. If you get the prop shop to do the calculations they may be a little more inclined to adjust the pitch
at a reasonable price
if the estimations are incorrect.
As an alternative, many feathering props have adjustable pitch. You still need to have the basics such as diameter correct, but there is usually easy adjustment of pitch. Your sailing speed will benefit, but they are not cheap