nesting boxes are often shared as the hens don't all lay at the same time. Also, often one or two particular nestboxes become the most popular and the chickens will 'stand in line' for the favorite or get in with another chicken..... I have 4 nesting boxes for 6 girls and one does not get used at all. If you have a broody sitting on eggs she should have her own 'private' spot I guess. I think the rule of thumb is 1 nesting box for ???2-4 hens....somebody please verify but I know that one nest per hen is not needed.
when we first started our coop i asked the same question.... 1 ft nesting boxes are good for 6 chickens... or so i read in a magazine... We have 21 chickens right now and we are doing a total of 4 nesting boxes... Much luck to u!