The average is 6 to 12 per litter (Can be more can be less)
The gestation is 21 to 23 days with the female being capable of being pregnant again within hours of giving birth.

So your total could be more but there are also other things you might take in consideration and that could lower your number if your breeders are house together at all time.

Communal breeding will lead to losses sometimes very little sometimes the entire litter

Back to back breeding will also take its toll on your females which could affect your production down the road.