How long do rats grow? - briefly
Rats attain full adult size in roughly five to six weeks, reaching a body length of 8–10 inches (20–25 cm) and a weight of 300–500 g. Growth slows markedly after this period, with only minimal size changes thereafter.
How long do rats grow? - in detail
Rats reach their full size within a predictable developmental window that varies by species and environmental conditions.
Newborn pups measure roughly 3–4 cm (1.2–1.6 in) in length and weigh 5–7 g. During the first week they double in weight, and by day 14 they attain approximately 30 g and a length of 7–9 cm (2.8–3.5 in).
Weaning occurs at 3–4 weeks of age; at this stage rats measure 12–15 cm (4.7–5.9 in) and weigh 70–100 g. Growth continues rapidly until sexual maturity, which is reached between 5 and 8 weeks for most laboratory and wild Norway (Rattus norvegicus) and black rats (Rattus rattus). Adult body length (head‑to‑base of tail) ranges from 20 to 25 cm (8–10 in), with total length including tail up to 40 cm (16 in). Typical adult weight falls between 250 and 500 g, though individuals in captivity with abundant food may exceed 600 g.
Factors influencing the growth timeline include:
- Genetics: Different strains exhibit distinct growth rates; dwarf laboratory strains mature faster but remain smaller.
- Nutrition: High‑calorie diets accelerate weight gain; protein deficiency slows skeletal development.
- Temperature: Ambient temperatures below 20 °C delay maturation, while optimal laboratory temperatures (22–24 °C) promote standard growth curves.
- Health status: Parasite load or disease can reduce both length and weight gain.
In summary, rats progress from birth to adult dimensions in roughly 5–8 weeks, with measurable milestones at 2 weeks (weaning) and 6 weeks (sexual maturity). Adult size stabilizes thereafter, subject to variations caused by genetics, diet, and environmental conditions.