The basic differences are similar for all species of hamsters, Syrian, dwarf, or Chinese.
Hold your hamster on its back to look at the belly area. You can cup your hand over your hamster and gently turn it over onto its back, or hold the hamster by the scruff. Holding the hamster in a slightly upright ("sitting up") position will help you determine if testicles are present.
The surest way to tell is by looking at the anogenital distance. This is the distance between the genital openings (penile opening in the male, vaginal and urinary openings in the female) and the anus. This distance is much shorter in females than males (in fact the openings can be difficult to distinguish in females while they are separated by about half an inch in males). This is illustrated in the diagram above.
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