Luter tun diameter of the holes

Hi guys!
Im going to make a lauter tun, consistin in to vessels, and i wonder wich diameter should have the holes that i would make in one of them.
Please help me.

1/8" ought to do it.  3mm if you’re a metric person.

Thanks man! Ill make them that size!

I ised the size you told me. Id allready made a batch and it worked perfectly, thanks again.