How much should a one-month-old rat weigh? - briefly
A rat that is four weeks old generally weighs between 30 g and 70 g, varying with strain and diet. Laboratory strains often fall near 50–60 g at this stage.
How much should a one-month-old rat weigh? - in detail
A rat that has reached the age of approximately four weeks should typically weigh between 80 g and 120 g. The exact value depends on several variables:
- Strain – Common laboratory strains such as Sprague‑Dawley or Wistar males often approach the upper end of the range, while females tend to be slightly lighter. Outbred pet rats may fall anywhere within the interval.
- Sex – Males generally gain weight faster and end up heavier than females of the same age.
- Nutrition – Access to a balanced diet of laboratory chow or high‑quality rodent pellets supports normal growth. Caloric restriction or poor food quality can reduce weight by 10 %–20 % compared with the expected range.
- Health status – Illness, parasitic infection, or chronic stress can cause weight loss or stunted gain. A healthy animal should gain roughly 20 g per week during the first month.
- Environmental factors – Ambient temperature, cage size, and enrichment affect metabolism; cooler environments may increase food intake and weight, while overcrowding can suppress growth.
Weight measurement should be performed with a calibrated digital scale capable of 0.1 g resolution. The animal should be weighed briefly in a clean container to minimize stress. Record the value daily or every other day to track growth trends.
If a four‑week‑old rat consistently measures below 70 g, investigate diet adequacy, screen for disease, and verify that the weighing equipment is accurate. Conversely, a weight exceeding 130 g may indicate obesity, which can predispose the animal to metabolic disorders and reduced lifespan.
Regular monitoring of body mass, combined with visual assessment of coat condition and activity level, provides a reliable indicator of developmental health during this critical growth phase.