How much should a pet rat weigh?

Adult female rats usually weigh 350–450 g (12–16 oz) and males 450–650 g (16–23 oz). Here's what's normal, how to weigh your rats, and why the trend matters more than any single number.

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What is a healthy weight for a rat?

According to the Merck Veterinary Manual, adult female rats typically weigh 350 to 450 g (12 to 16 oz) and adult males 450 to 650 g (16 to 23 oz). Young rats are still growing, and rats vary in build, so a rat a little outside these ranges isn't necessarily unhealthy. Your vet can tell you whether your rat's body condition is right for them.

How often should I weigh my rat?

The RSPCA advises weighing rats regularly, to make sure they aren't rapidly gaining or losing weight. A kitchen scale works well: put a small box or bowl on it, reset it to zero, then pop your rat in and note the number.

Why does weight loss matter?

Losing weight, or quickly putting weight on, is on the RSPCA's list of signs that a rat may be ill or in pain, and the PDSA lists weight loss among the symptoms of respiratory disease. Weight loss is often the first sign of illness that owners notice, so a scale can show a problem before your eyes do. See signs your rat is sick for what else to watch for.

What if my rat is overweight?

Rats gain weight easily. The PDSA advises following the feeding guidelines on the packet and weighing the food out each day, and the RSPCA warns that too much sugar and fat leads to obesity and health problems — fresh foods and treats should come out of the daily allowance, not on top of it. See what to feed pet rats, and ask a vet before putting a rat on a diet.