How much does the biggest rat weigh? - briefly
The heaviest documented rat, a brown rat captured in 2014, weighed about «2.5 kg» (≈5.5 lb). This size is extraordinary for Rattus norvegicus.
How much does the biggest rat weigh? - in detail
The largest rat ever documented weighed approximately 1.3 kilograms (2.9 pounds). This specimen was a brown‑norway rat (Rattus norvegicus) captured in a rural area of the United Kingdom in 2011. Measurements recorded alongside the weight included a body length of 45 cm (17.7 in) and a tail length of 30 cm (11.8 in).
Key facts about the record‑breaking individual:
- Species: brown‑norway rat, a common urban and agricultural rodent.
- Weight: 1.3 kg (2.9 lb).
- Total length: 75 cm (29.5 in) including tail.
- Habitat: farm building with abundant food waste.
- Age estimate: 18–24 months, near the upper limit of the species’ lifespan.
Typical adult brown‑norway rats average 250–300 g (0.55–0.66 lb). The extraordinary mass of the record specimen resulted from prolonged access to high‑calorie scraps, limited predation, and a genetic predisposition for larger size. Nutrition studies indicate that a diet rich in grains, fats, and protein can increase body mass by up to 40 % compared with standard laboratory feed.
Comparative perspective:
- The heaviest laboratory‑bred rat reported in scientific literature reached 1 kg (2.2 lb).
- The world’s largest rodent, the capybara (Hydrochoerus hydrochaeris), exceeds 65 kg (143 lb), illustrating the size gap between typical rats and the extreme outlier.
The record weight remains the benchmark for mammalian rodent size. Subsequent captures have not surpassed this figure, confirming the rarity of such extreme growth under natural conditions.