Karel Busta

Fact

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: SolidReplicated or measured directly in a large, well-designed sample.
Daily sleep vs body weight, 83 mammal speciesTotal sleep per day (h) vs body weight (kg, log scale)
Show the data as a table
nameBody weight (kg, log scale)Total sleep per day
Cheetah5012.1 h
Owl monkey0.4817 h
Mountain beaver1.3514.4 h
Greater short-tailed shrew0.0214.9 h
Cow6004 h
Three-toed sloth3.8514.4 h
Northern fur seal20.498.7 h
Vesper mouse0.057 h
Dog1410.1 h
Roe deer14.83 h
Goat33.55.3 h
Guinea pig0.739.4 h
Grivet4.7510 h
Chinchilla0.4212.5 h
Star-nosed mole0.0610.3 h
African giant pouched rat18.3 h
Lesser short-tailed shrew0.019.1 h
Long-nosed armadillo3.517.4 h
Tree hyrax2.955.3 h
North American Opossum1.718 h
Asian elephant2,5473.9 h
Big brown bat0.0219.7 h
Horse5212.9 h
Donkey1873.1 h
European hedgehog0.7710.1 h
Patas monkey1010.9 h
Western american chipmunk0.0714.9 h
Domestic cat3.312.5 h
Galago0.29.8 h
Giraffe9001.9 h
Pilot whale8002.7 h
Gray seal856.2 h
Gray hyrax2.636.3 h
Human628 h
Mongoose lemur1.679.5 h
African elephant6,6543.3 h
Thick-tailed opposum0.3719.4 h
Macaque6.810.1 h
Mongolian gerbil0.0514.2 h
Golden hamster0.1214.3 h
Vole0.0412.8 h
House mouse0.0212.5 h
Little brown bat0.0119.9 h
Round-tailed muskrat0.2714.6 h
Slow loris1.411 h
Degu0.217.7 h
Northern grasshopper mouse0.0314.5 h
Rabbit2.58.4 h
Sheep55.53.8 h
Chimpanzee52.29.7 h
Tiger162.5615.8 h
Jaguar10010.4 h
Lion161.513.5 h
Baboon25.249.4 h
Desert hedgehog0.5510.3 h
Potto1.111 h
Deer mouse0.0211.5 h
Phalanger1.6213.7 h
Caspian seal863.5 h
Common porpoise53.185.6 h
Potoroo1.111.1 h
Giant armadillo6018.1 h
Rock hyrax3.65.4 h
Laboratory rat0.3213 h
African striped mouse0.048.7 h
Squirrel monkey0.749.6 h
Eastern american mole0.088.4 h
Cotton rat0.1511.3 h
Mole rat0.1210.6 h
Arctic ground squirrel0.9216.6 h
Thirteen-lined ground squirrel0.113.8 h
Golden-mantled ground squirrel0.2115.9 h
Musk shrew0.0512.8 h
Pig86.259.1 h
Short-nosed echidna4.58.6 h
Eastern american chipmunk0.1115.8 h
Brazilian tapir207.54.4 h
Tenrec0.915.6 h
Tree shrew0.18.9 h
Bottle-nosed dolphin173.335.2 h
Genet26.3 h
Arctic fox3.3812.5 h
Red fox4.239.8 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.

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.

Source and method

  1. Savage VM, West GB (2007). A quantitative, theoretical framework for understanding mammalian sleep. Proceedings of the National Academy of SciencesSample: 83 mammal species (sleep times compiled from Zepelin 1989)

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.

Published October 14, 2026.

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