Floor space is the only number that really counts
Dwarf hamsters — Campbell's, winter whites, Roborovskis and their hybrids — may be a third of a Syrian's length, but they range like animals twice their size, covering long distances across open ground in a night. That is why cage size for a dwarf is measured in unbroken floor: a rectangle of at least eighty by fifty centimetres is the floor a dwarf needs to run, forage, dig and arrange a nest with room to spare, and a metre by fifty gives a visibly more relaxed animal with space for every piece of equipment without crowding. Height, by contrast, buys a dwarf almost nothing. They climb poorly and fall badly, so a low, wide enclosure beats a tall narrow one every time.
Ignore the way small cages are marketed in modules. Two or three little plastic pods linked by tubes are sold as expandable luxury, but a dwarf experiences them as small rooms and corridors — there is no stretch of ground anywhere in the system big enough to behave naturally on, and the tubes themselves are awkward for a round little animal to climb, easy to block with bedding, and a nuisance to clean.
Bars a dwarf cannot pour himself through
A dwarf hamster's skull is the only rigid measurement he cannot reduce; the rest of him pours. Bar spacing of a centimetre or less keeps a dwarf in; spacing much beyond that has lost more hamsters than any other single cage fault, usually overnight and usually discovered by the bedding rustling somewhere it should not. If the cage you love has wider bars, the honest options are a different cage, or meshing the whole thing over — a fiddly job that needs every edge checked, because the one loose corner is the one he will find.
Tank-style enclosures sidestep the problem entirely and bring their own advantages: glass or clear acrylic walls cannot be climbed or chewed, bedding stays inside instead of being kicked through bars, and the deep fill a dwarf needs does not end up across your floor. Ventilation comes from a meshed lid, which must be fine-meshed and firmly fitted — the lid is the tank's equivalent of bar spacing.
Depth for burrowing beats height for climbing
Budget the cage's depth for bedding, not its height for levels. A dwarf should have a deep end of bedding he can vanish into completely — a burrow system with the nest at the bottom is how he is built to sleep — so choose an enclosure whose base or tank walls let you fill one end generously deep while keeping a shallower foraging area at the other. Platforms, if you add any, stay low, close to the bedding surface, and reached by ramps rather than ladders; a dwarf falling a short way onto deep bedding is unharmed, while falls onto hard surfaces from cage-top height are a different story.
The wheel makes the same point about honest sizing: around twenty centimetres across, solid-surfaced, so a running dwarf's back stays flat rather than curving up into the wheel. A wheel that is too small is worse than none, and a dwarf will still use it nightly and quietly strain himself doing so.
One space, everything in it, room left over
Lay the enclosure out as one landscape: deep bedding at the sleeping end, a sand bath in a sturdy dish — dwarfs roll in sand to keep their coats in order — the wheel on the shallower ground, a hide or two, and open floor threading between them. If everything essential fills the floor completely, the cage is too small whatever the tape measure said, because the running room was the point.
Write the floor dimensions and bar spacing on your dwarf hamster's KinsLe profile through Family Sharing before you ever need a second enclosure, and whoever in the family buys the travel cage or the upgrade checks the numbers that keep him in and give him ground to range, instead of being charmed by a smaller box with better colours.