40 gallon breeder ?

So how many mice would you say would fit nicely in a 40 gallon breeder. I jst got one for free off craigslist. And want to get some mice to put in there also should there only be one male or couls i get away with a couple since there will be so many girls...

You would only need one male. Putting in another is an un-necessary risk.

I would say you could comfortably put 10-15 females, and one male. If it starts to look crowded though, take some out.

Adding in some popsicle stick platforms or cardboard boxes and hiding places, will make the tank hold more mice, and you could definitely do 15. But just flat floor with litter may only hold closer to 10.