5 things that help you upgrade a cage that's too small

A cage sized for the animal pictured on the packaging almost never matches the cage that animal needs as an adult. Most pet-shop housing is marketed with young, half-grown stock, and the litres printed on the box count ramps and roof height the animal barely uses day to day. RSPCA and PDSA guidance measure in floor space for exactly this reason: a rabbit needs room to stand fully upright on its hind legs without its ears brushing the roof and take at least three hops in a row, and a single guinea pig needs roughly 7.5 sq ft of continuous floor — more for a bonded pair, and pairs are recommended. Extra levels and ramps rarely make up a shortfall in that number; they mostly create dead space underneath and a fall risk on the way down, so it's floor space your upgrade budget should go on, not another shelf.

A cube-and-coroplast (C&C) grid gets you two or three times the floor space of a shop-bought hutch for a fraction of the price. You're buying flat-pack storage cubes and a sheet of corrugated plastic, not a company's branding and moulded-plastic markup — it's the setup the online guinea pig and rabbit community switched to years ago, precisely because commercial cages never caught up with what welfare guidance actually asks for. The grid scales, too: add another row of cubes when you take in a foster or lose a cage-mate, instead of buying a whole new cage.

A large opaque storage tote gives a hamster far more usable floor and digging depth than almost any shop cage. Most retail 'hamster starter kits' cap out at a shelf-friendly footprint with barely a cereal bowl's depth of substrate, while a hamster's instinct is to tunnel down 25-30cm or more — and height and genuinely secure sides matter as much as floor area. My last foster hamster, Custard, escaped two 'secure' shop cages before I built her a bin cage; she never got anywhere near the top of that one. For rats, size up and keep them in pairs with connecting tubing — they're social, and a lone rat in a bigger box hasn't actually solved the problem.

Reptile and bird enclosures sized for what an adult actually needs are hugely overpriced new, but turn up secondhand constantly. Most keepers buy the cute juvenile-sized setup and then have to upgrade within a year once the animal outgrows it — an adult bearded dragon needs a minimum footprint of around 4ft x 2ft, which almost no beginner kit provides, and I learned that the expensive way with my own beardie. People rehoming a reptile or downsizing an aviary are usually just relieved to see it go to someone who'll use it properly, so glass vivs, mesh flight cages and whole rabbit runs turn up for a fraction of retail, sometimes free. Buying the enclosure and any accessories as separate purchases, rather than a shrink-wrapped 'starter kit', is almost always both bigger and cheaper.

A prey animal moved straight into a completely unfamiliar space with none of its own scent in it reads the change as a threat, not an upgrade. That stress alone is sometimes enough to put a rabbit or guinea pig off its food, so carrying over unwashed bedding, hides and even a rubbed-on cloth from the old cage means the new space smells partly like home from hour one instead of like something to investigate all night. Set the new enclosure up three to five days ahead in the same room, so the animal isn't dealing with a new smell and a new size on the same day.