What size cage do two guinea pigs need?

For two guinea pigs you need a minimum space of 120x60 cm, or better yet 150x75 cm if you can manage it. It's not an arbitrary size: these animals need space to move around, get exercise, and have some distance from each other when they want it. A small cage causes stress and behavioral problems, plus health issues.

Inside the cage organize different "zones": one for food and water, one for hay (they eat a lot of it), one with hiding spots. Guinea pigs love tunnels and little houses where they can retreat, so include at least a couple of these elements. The bedding should be a few centimeters deep (recycled paper or hay work fine), and you need to change it regularly because these little guys produce quite a bit of mess.

On the practical side: the cage should be in a ventilated spot but without direct drafts, away from too much direct sunlight and loud noises. If you live in an apartment, avoid the kitchen (stove fumes aren't great for them). And give them access to some outside space every once in a while if you can, because being in the cage all the time isn't ideal. With these precautions your guinea pigs will do much better.