How long does a rat grow? - briefly
Rats reach adult size in about five to six weeks, attaining a body length of roughly 9–11 cm (3.5–4.5 in) with a tail of comparable length.
How long does a rat grow? - in detail
Rats reach their full size within a relatively short interval after birth. Newborn individuals weigh between five and seven grams and measure roughly five to seven centimeters in total length, including the tail. The first developmental milestone is weaning, which occurs at three to four weeks of age; at this point, juveniles begin to consume solid food independently and show a rapid increase in body mass, typically gaining 10–15 % of their adult weight each week.
Puberty follows shortly after weaning, appearing around five to six weeks. Hormonal changes, especially the surge of testosterone in males and estrogen in females, trigger the development of secondary sexual characteristics and accelerate skeletal growth. By eight to ten weeks, most rats have attained their adult dimensions. For the common Norway rat (Rattus norvegicus), adult weight ranges from 250 g to 500 g, and total length, tail included, reaches 20–25 cm. Black rats (Rattus rattus) are slightly smaller, averaging 150–250 g with a total length of 16–20 cm.
Growth continues at a diminishing rate until approximately twelve weeks, after which weight stabilizes and only minor fluctuations occur due to health status, diet, and environment. Factors influencing the growth timeline include:
- Genetic strain: laboratory strains often exhibit faster, more uniform growth than wild populations.
- Nutritional quality: protein‑rich diets accelerate muscle development and overall mass gain.
- Ambient temperature: cooler conditions can slow metabolism, extending the growth period.
- Health conditions: disease or parasitic load can impede normal weight gain.
In summary, rats progress from birth to adult size in roughly two to three months, with the most pronounced growth phases occurring between the third and tenth weeks of life. The exact duration and final dimensions depend on species, genetics, and environmental conditions.