# The bigger the mammal, the less it sleeps

> Across 83 mammal species, every tenfold increase in body weight goes with about 21% less daily sleep (log-log slope −0.103, 95% CI −0.130 to −0.075, R² = 0.40). A 1 kg mammal is predicted to sleep about 10.1 hours; a giraffe actually logs 1.9.

Confidence: **solid**. Published 2026-10-14. Canonical: https://karelbusta.dev/data/sleep/bigger-animals-sleep-less

Little brown bats sleep 19.9 hours a day; giraffes 1.9. Body size explains about 40% of that spread: big grazers like horses, cows and elephants sit at the bottom, small bats, opossums and rodents at the top. Savage and West tie this to metabolism: per gram, small brains run hotter, and their model treats sleep as time for repair. Two caveats matter: almost all of these numbers come from captive or laboratory animals, and wild animals can sleep very differently (wild elephants manage about 2 hours, wild sloths about 9.6 rather than the 14+ hours reported in captivity). Size is a strong trend, not a rule: the tiger (15.8 h) and the giant armadillo (18.1 h) are heavy and still sleep a lot.

## Daily sleep vs body weight, 83 mammal species

| name | Body weight (kg, log scale) | Total sleep per day |
| --- | --- | --- |
| Cheetah | 50 | 12.1 h |
| Owl monkey | 0.48 | 17 h |
| Mountain beaver | 1.35 | 14.4 h |
| Greater short-tailed shrew | 0.019 | 14.9 h |
| Cow | 600 | 4 h |
| Three-toed sloth | 3.85 | 14.4 h |
| Northern fur seal | 20.49 | 8.7 h |
| Vesper mouse | 0.045 | 7 h |
| Dog | 14 | 10.1 h |
| Roe deer | 14.8 | 3 h |
| Goat | 33.5 | 5.3 h |
| Guinea pig | 0.728 | 9.4 h |
| Grivet | 4.75 | 10 h |
| Chinchilla | 0.42 | 12.5 h |
| Star-nosed mole | 0.06 | 10.3 h |
| African giant pouched rat | 1 | 8.3 h |
| Lesser short-tailed shrew | 0.005 | 9.1 h |
| Long-nosed armadillo | 3.5 | 17.4 h |
| Tree hyrax | 2.95 | 5.3 h |
| North American Opossum | 1.7 | 18 h |
| Asian elephant | 2547 | 3.9 h |
| Big brown bat | 0.023 | 19.7 h |
| Horse | 521 | 2.9 h |
| Donkey | 187 | 3.1 h |
| European hedgehog | 0.77 | 10.1 h |
| Patas monkey | 10 | 10.9 h |
| Western american chipmunk | 0.071 | 14.9 h |
| Domestic cat | 3.3 | 12.5 h |
| Galago | 0.2 | 9.8 h |
| Giraffe | 899.995 | 1.9 h |
| Pilot whale | 800 | 2.7 h |
| Gray seal | 85 | 6.2 h |
| Gray hyrax | 2.625 | 6.3 h |
| Human | 62 | 8 h |
| Mongoose lemur | 1.67 | 9.5 h |
| African elephant | 6654 | 3.3 h |
| Thick-tailed opposum | 0.37 | 19.4 h |
| Macaque | 6.8 | 10.1 h |
| Mongolian gerbil | 0.053 | 14.2 h |
| Golden hamster | 0.12 | 14.3 h |
| Vole | 0.035 | 12.8 h |
| House mouse | 0.022 | 12.5 h |
| Little brown bat | 0.01 | 19.9 h |
| Round-tailed muskrat | 0.266 | 14.6 h |
| Slow loris | 1.4 | 11 h |
| Degu | 0.21 | 7.7 h |
| Northern grasshopper mouse | 0.028 | 14.5 h |
| Rabbit | 2.5 | 8.4 h |
| Sheep | 55.5 | 3.8 h |
| Chimpanzee | 52.2 | 9.7 h |
| Tiger | 162.564 | 15.8 h |
| Jaguar | 100 | 10.4 h |
| Lion | 161.499 | 13.5 h |
| Baboon | 25.235 | 9.4 h |
| Desert hedgehog | 0.55 | 10.3 h |
| Potto | 1.1 | 11 h |
| Deer mouse | 0.021 | 11.5 h |
| Phalanger | 1.62 | 13.7 h |
| Caspian seal | 86 | 3.5 h |
| Common porpoise | 53.18 | 5.6 h |
| Potoroo | 1.1 | 11.1 h |
| Giant armadillo | 60 | 18.1 h |
| Rock hyrax | 3.6 | 5.4 h |
| Laboratory rat | 0.32 | 13 h |
| African striped mouse | 0.044 | 8.7 h |
| Squirrel monkey | 0.743 | 9.6 h |
| Eastern american mole | 0.075 | 8.4 h |
| Cotton rat | 0.148 | 11.3 h |
| Mole rat | 0.122 | 10.6 h |
| Arctic ground squirrel | 0.92 | 16.6 h |
| Thirteen-lined ground squirrel | 0.101 | 13.8 h |
| Golden-mantled ground squirrel | 0.205 | 15.9 h |
| Musk shrew | 0.048 | 12.8 h |
| Pig | 86.25 | 9.1 h |
| Short-nosed echidna | 4.5 | 8.6 h |
| Eastern american chipmunk | 0.112 | 15.8 h |
| Brazilian tapir | 207.501 | 4.4 h |
| Tenrec | 0.9 | 15.6 h |
| Tree shrew | 0.104 | 8.9 h |
| Bottle-nosed dolphin | 173.33 | 5.2 h |
| Genet | 2 | 6.3 h |
| Arctic fox | 3.38 | 12.5 h |
| Red fox | 4.23 | 9.8 h |

All 83 species in the mammal-sleep dataset (Savage & West 2007 via ggplot2 msleep). The fit statistics are in the dataset's allometry table.

## Sources

- Savage VM, West GB (2007) [A quantitative, theoretical framework for understanding mammalian sleep](https://doi.org/10.1073/pnas.0610080104) Proceedings of the National Academy of Sciences. Sample: 83 mammal species (sleep times compiled from Zepelin 1989)

## Method

Ordinary least squares fit of log10(total sleep, h/day) on log10(body weight, kg) for all 83 species in the mammal-sleep dataset, computed by this site's ingest script (apps/data/ingest/mammal-sleep/build.ts). Savage & West report the same exponent for total sleep time (about −0.1); their headline −0.16 exponent is for the ratio of sleep to waking time, not total sleep. Dropping the three whales and dolphins whose sleep the authors halved (n = 80) gives a slope of −0.096 and R² = 0.36.

Dataset: [Sleep in mammals](https://karelbusta.dev/data/sleep/datasets/mammal-sleep)

Ranking: [Which animals sleep the most?](https://karelbusta.dev/data/sleep/animals-that-sleep-the-most)

## Related facts

- [Wild elephants sleep about 2 hours a day](https://karelbusta.dev/data/sleep/wild-elephants-sleep-2-hours)
- [Frigatebirds sleep in mid-air, about 40 minutes a day](https://karelbusta.dev/data/sleep/frigatebirds-sleep-in-flight)
- [People living without electricity don't sleep more than we do](https://karelbusta.dev/data/sleep/hunter-gatherers-sleep-less)