These are guidelines to the average rat:

Adult Weight:      

Does: between 250 to 500g, average of 300g (10.5oz)

Bucks: Between 450 and 750g, average of 500g (17.5oz)

Life Span

A very sad 2.5 to 4 years.

Body Temperature

37.5 to 38 degrees C, 99.5 to 100 degrees F

Duration of mating period

Between 9 and 20 hours, although the actual

 copulation itself takes a matter of seconds

Respiratory rate

From 70 to 150 breaths a minute

Heart rate

From 250 to 450 BPM

Gap between mating periods

5 days

Gestation 

21 to 23 days

Litter size 

From 6 to 12 but on occasion as many as 18

Eyes open at 

10 to 12 days old

Nursing period 

21 days

Eating solid food at 

10 to 12 days

Sexual maturity 

65 to 110 days

Breeding life 

Up to 18 months although first litters should never be later

than 9 or 10 months of age for the safety of the rat.

Not all rats will conform to these ideals, there are always exceptions to any rule,

these are merely guidelines.