Even though hamsters are very small they actually require a lot of space, it is not uncommon for hamsters in the wild to run 9km in one night. The Veterinary Association for Animal Welfare is Headquartered in Frankfurt and was established in 1985 by 150 veterinarians, also known as (TVT). They recommend the cage size should be at “minimum 100cm x 50cm x 50cm (L x W x H) which is 5000 cm2 (775 in2)” this is also referred to on Wikipedia. This is the minimum recommended cage size for ALL species of hamsters including Dwarf. Please note this is a minimum of unbroken floor space (not levels), the more space the better.
Don’t be fooled by what the pet shops recommend. Pet shops usually always sell cages which are far too small, this is because they are often cheaper for customers to buy and they save on shop floor space. If you buy a cage which is too small, your hamster will sadly live a miserable life.