from wikipedia
general rule of thumb is that a mammal
will produce half as many offspring
as the number
of teats on the mother.
This rule is altered in domesticated animals
since larger litters are
often favoured for economic reasons
and in dogs, particularly,
the great range of sizes and shapes plays
a role in how many
healthy
puppies a female can carry.
An average litter consists
of about six puppies, though this number may vary widely based on
the breed of dog.
Toy dogs generally produce from one to four puppies
in each litter.
The number of puppies also varies with the mother's age
and health, the father's sperm count, the timing of the breeding,
and many other factors.