If I have 10 chickens how big does the coop have to be?

need 4sq feet per bird

 

3 sq foot for silkies 4 sq foot for standards

 

You will have a run, also, yes?, so we're just talking about *indoor* space here?

Normally I would say 40 sq ft would do ya, but you may want to go a bit bigger than that. Two reasons: mature broilers are BIIIIIIIG (be aware they do not live normal lifespans, and if they are pets I hope you are restricting their feed and providing ample exercise), and also most people end up getting more chickens later on.

It also depends on your climate. If it's nice year-round and the birds will have access to a good-quality run with some shelter in it and good (not horribly swampy) footing, you can stick with a smaller size coop (if you really insist) than if you are somewhere with long stretches of weather in which the chickens may not be wanting to spend lotsa time outside.

Have fun,

Pat