* Age of the mother: Younger dogs tend to have larger litters than older dogs.
* Breed size: Jack Russell Terriers are generally small to medium-sized dogs.
* Individual dog's health: A healthy mother will likely have a larger litter than a dog with health issues.
* Number of previous litters: A dog that has had multiple litters in the past may have smaller litters in the future.
On average, a Jack Russell Terrier can have a litter of 3 to 6 puppies. However, some litters can be as small as 1 puppy or as large as 10 or more.