The smaller hamster breeds eat less than the larger Syrian hamster. But roughly speaking, hamsters need just one or two teaspoons of dry food a day. If you notice large amounts of dry food in the hamster's bedding, you're probably feeding too much. If, on the other hand, the food disappears very quickly, you should increase the amount slightly.
Hamsters only need small amounts of food
If your hamsters are a Dwarf variety such as the Roborovskis (as in the photo above), less than one teaspoon will be enough. Pregnant or recuperating hamsters require more food than usual, including a little extra protein. Use your judgement and adjust the amounts based on your observations, on a pet-by-pet basis.