size of a hedgehog door

[PigletJohn]

I am rebuilding a fence. It has concrete gravel boards. At one end I want to put a gap at ground level for hedgehogs. How big should it be?

I read in a book yesterday that it should be 10cm square. Mainly, too small for cats to get through or for them to get their heads stuck in. I will be ensuring I have some too, so was wondering the same thing. Perhaps someone has better experience with hedgehog doors and winter homes.

thanks!

I also found some doorway signs to discourage people from blocking them up.

(that's not my fence)

Try also the experts at www.hedgehogstreet.org. Let us know what you find.