How much does an average rat weigh? - briefly
An adult laboratory rat typically weighs 250–350 g, while a common wild brown rat ranges from 150–300 g. These figures represent the usual weight range for a mature «average rat».
How much does an average rat weigh? - in detail
The common brown rat (Rattus norvegicus) typically reaches a body mass between 250 g and 450 g in adulthood. Male individuals generally occupy the upper portion of this interval, while females are usually found toward the lower end.
Key factors influencing weight include:
- Sex: males heavier than females by approximately 20–30 %
- Age: juveniles under 100 g, adults reaching full size after 8–10 weeks
- Diet: high‑calorie feed increases mass; restricted diets produce lighter specimens
- Health status: parasites or illness can reduce body weight
- Strain: laboratory lines (e.g., Sprague‑Dawley, Wistar) often weigh less than wild counterparts
Wild rats exhibit broader variability, with recorded weights ranging from 150 g for small, newly weaned individuals to over 600 g for exceptionally large, well‑fed adults. Laboratory rats, maintained under controlled conditions, display tighter ranges, commonly 300–350 g for males and 250–300 g for females.
Weight conversions commonly used in research:
- 1 g ≈ 0.035 oz
- 100 g ≈ 3.5 oz
- 300 g ≈ 10.6 oz
These figures support precise dosing calculations for pharmacological studies, where drug volume is often expressed per kilogram of body weight. Accurate measurement requires a calibrated digital balance, recording to the nearest 0.1 g.
In summary, the average adult brown rat weighs roughly three to four hundred grams, with variations dictated by sex, age, nutritional regimen, health, and whether the animal originates from a wild population or a laboratory breeding program.