What is the average weight of a rat? - briefly
Adult laboratory rats generally weigh 250–300 g, while wild individuals can range from about 150 g to 500 g depending on species and nutrition.
What is the average weight of a rat? - in detail
Rats exhibit a broad range of body masses depending on species, sex, age, and living conditions. Laboratory strains such as the Sprague‑Dawley or Wistar typically weigh between 250 g and 350 g for adult males and 200 g to 300 g for adult females. Wild brown rats (Rattus norvegicus) commonly fall within 300 g to 500 g, with larger individuals reaching up to 600 g in resource‑rich environments. Juvenile rats increase rapidly: newborns weigh about 5 g, and by four weeks of age they approach 100 g.
Key factors influencing weight:
- Genetics: Inbred laboratory lines have reduced variability; outbred or wild populations show greater dispersion.
- Nutrition: High‑calorie diets accelerate growth and elevate adult mass; restricted feeding produces leaner subjects.
- Health status: Parasite load, disease, and stress can cause weight loss or abnormal gain.
- Housing conditions: Group housing may lead to competition for food, affecting individual weights.
Measurement standards recommend using a calibrated analytical balance, recording mass to the nearest gram for adult rats and to 0.1 g for juveniles. Data are typically expressed as mean ± standard deviation; for example, a study of 120 adult Sprague‑Dawley males reported 312 ± 22 g.
When comparing across studies, ensure consistent units (grams or kilograms) and specify whether the reported value represents live weight, post‑mortem carcass weight, or dry weight, as each metric differs by 5–10 %.