Are two roosters OK for a flock of 20 hens?

[americana-chick]

I have 3 roos for about 20 hens and all is going well

 

[Mahonri]

I should probably put another roo in my main coop. He's in there with 19 girls.

 

[rittert3]

I read in my guide to better hatching book (by, I believe, Janet stromberg) that there was a college study done on RIRs and the peek fertility was at 1 roo to 9 hens, but your ratio should be fairly good with 2:20