What size pop door for Standard Cochins?

[Shkittles]

we should be finished with the run tomorrow and need to know how big of a whole to make so that our 4 Standard Cochins can fit through it and get in the run. If our Cochins can fit through it all our other chickens should be able to.

Thanks,
!Shkittles!

 

[rittert3]

Same question, I was planning on a 18" high by 12"wide Guilitien style door (maybe the same thing?) but not 100% sure this is the correct size.