How much does a large rat weigh? - briefly
A fully grown large rat typically weighs between 300 g and 500 g (approximately 0.7–1.1 lb), with exceptionally large individuals reaching up to 1 kg. This range reflects normal adult body mass for the species.
How much does a large rat weigh? - in detail
A mature Norway rat (Rattus norvegicus) that has reached its maximum size typically weighs between 350 g and 500 g (12–18 oz). Exceptional individuals, especially those kept as pets and fed a high‑calorie diet, can exceed 600 g (about 1.3 lb). Wild specimens are generally lighter, averaging 300–400 g, because limited food availability restricts growth.
Factors influencing the final mass include:
- Sex: Males are on average 10‑15 % heavier than females.
- Age: Weight increases rapidly during the first three months, then plateaus.
- Genetics: Certain laboratory strains (e.g., Sprague‑Dawley) have been bred for larger body size.
- Nutrition: High‑fat or high‑protein diets add 20‑30 % to body mass compared with a standard grain‑based regimen.
- Health status: Parasitic load or chronic disease can reduce weight by up to 25 %.
Measurement is most accurate when the animal is gently restrained and placed on a calibrated digital scale with a capacity of at least 1 kg and a resolution of 1 g. Weighing should be performed after a short fasting period (3–4 h) to minimize gastrointestinal content variability.
For comparative context, a typical house mouse (Mus musculus) weighs 20–30 g, while a brown squirrel can reach 500–700 g. Thus, a fully grown large rat occupies the intermediate weight range among common rodents, making it a useful model for biomedical research where body mass approximates that of small mammals such as guinea pigs.