Before breeding hamsters consideration should be given to what is to be done with the babies. Local pet shops may be willing to take surplus babies but it is best to ask before making the decision to breed your hamsters.
Although the average litter size for a Syrian hamster is 8 they can have up to 18 babies and Dwarf hamsters average a litter of 4 but can have up to 14.
Due to the fact that most hamsters kept as pets are from different genus and different species they will not (and are not able to) interbreed.
Dwarf hamsters are easy to breed due to the fact that they live together. Mixed sex pairs or groups will almost certainly breed. Dwarf hamsters can start breeding as young as 2-3 months of age (Roborovski hamsters do not usually start until breeding much later) and the gestation period is 18-21 days (or 23-30 days for Roborovski hamsters).
Syrian hamsters are able to breed as young as 3-5 weeks of age, the ideal age to breed a female for the first time is 4-6 months of age. Breeding a female younger than this can stunt her growth, result in a poor litter and often leads to cannibalism of the litter.
To sex a hamster you need to be able to look at its genitals. This can be done in one of two ways:
1.) Place the hamster on one hand, place your other hand over it's
back and turn your hands over so that the hamster is lying on it's back.
2.) Hold the hamster by the scruff of the neck in order to see underneath.
The concept of sexing any species of hamster is the same. The male is more elongated around the rear and more rounded than the female and this is particularly noticeable with Chinese Hamsters.
Looking at the genitals there are two 'vents' - on the male these are the penile opening and the anus, and on the female these are the vagina and the anus. The gap between these two vents on the male is usually 1-2cm apart (Dwarf-Syrian) and on a female the gap is so small that it is difficult to distinguish the two separate vents.