size of nestbox entrance?

[Caju]

I want to make the nestbox area dark, since the henhouse will be pretty light. I thought I'd make a partial wall with round entrance holes. The bottom part will be a false front attached to a bottom board so I can pull it out and clean out the nesting materials. Eggs will be collected from an outside lid.

What is the smallest entrance hole I can make that will still be comfortable for regular size (not bantam) hens?

https://www.backyardchickens.com/forum/uploads/48269_2010_earlymarch_007.jpg
https://www.backyardchickens.com/forum/uploads/48269_2010_earlymarch_018.jpg

 

[CoopCrazy]

I would think an 8 inch round would be plenty big enough but not sure...