Roughly how many hours a day does a koala typically sleep?

Koalas sleep roughly 18 to 20 hours a day, making them among the sleepiest mammals on Earth. The main driver is their diet: eucalyptus leaves are tough, fibrous, and mildly toxic, providing very little usable energy once digested. A koala's body compensates by minimizing activity, spending almost all its waking time simply chewing more leaves rather than moving, socializing, or exploring.

Eight hours is closer to typical human sleep, far too little to match a koala's extreme low-energy lifestyle. Twelve hours undercounts it too — that would suit a more active grazer, not an animal whose entire diet forces near-constant rest just to conserve calories.

Koalas even have unusually small brains relative to body size compared with other marsupials, and some researchers suspect this also helps limit energy demand, letting the animal survive on a food source most other mammals could never subsist on.