Which is larger, a rat or a mouse? - briefly
Rats exceed mice in size, with adult bodies usually 20–30 cm long and weighing 200–500 g, while mice average 7–10 cm and 15–30 g. This size difference is consistent across common species.
Which is larger, a rat or a mouse? - in detail
Rats consistently exceed mice in overall dimensions. Adult brown rats (Rattus norvegicus) typically weigh 250–500 g and measure 20–25 cm in body length, with tails adding another 18–25 cm. In contrast, common house mice (Mus musculus) average 15–30 g, with body lengths of 7–10 cm and tails of similar length.
Key size metrics:
- Body mass: Rat ≈ 250–500 g; Mouse ≈ 15–30 g.
- Body length (head‑to‑base): Rat ≈ 20–25 cm; Mouse ≈ 7–10 cm.
- Tail length: Rat ≈ 18–25 cm; Mouse ≈ 7–10 cm.
- Overall length (including tail): Rat ≈ 38–50 cm; Mouse ≈ 14–20 cm.
Growth patterns differ. Rats reach sexual maturity at 5–6 weeks, achieving adult size by 2–3 months. Mice mature faster, becoming reproductively active at 4–5 weeks, but remain substantially smaller throughout life.
Species variation influences size. Larger rat species, such as the black rat (Rattus rattus), still surpass the largest mouse species, including the African pygmy mouse (Mus minutoides), which rarely exceeds 10 g and 5 cm total length.
Therefore, across all standard laboratory and wild populations, the rodent classified as a rat is markedly larger than any mouse in terms of mass, body length, and tail length.