Okay let's do a little rat stages of life thing LOL....

Rats are born as "pinks"....this is the stage when they have no hair, their eyes are shut and their ears are tight to the head....they depend totally on the female rat for her milk and for life...these are newborn pinkie rats...


At around day 8 of life they start to develop their first coat, a tight to the body, satin looking coat and are referred to as "fuzzies"....their eyes are still closed, their ears are tight to the skull...they still only take in mother's milk for nutrition...these are fuzzy rats...


About day 15 they become "pups", their eyes open, their ears become erect and they develop a full coat of fur.....they will start to follow mother rat to her food bowl and try her water bottle (usually by day 20 or so, some try earlier)...they still need to nurse however....this is a young rat pup whose eyes have just opened....


As they approach weaning at about 4 or 5 weeks of age (some wean as early as 3.5 weeks) they become quite large pups, as soon as they are weaned they are "weanlings" or "wean rats".....here is a picture of a litter that I weaned off their mother just after this picture was taken so this is basically a group of nice wean rats....notice how much they grow during the pup stage...at this stage they no longer need their mother's milk but will continue to bother her for nursing...they really need to be independent and seperated by gender no later than 5 weeks of age.....


This is another example of a recently weaned rat...


Same male rat a couple of weeks later when he is big enough to be no longer considered a weanling rat...


Example to show size differences...the right on the left is a breeding size female...I would call her a medium in size....to the right is a younger female, not yet to breeding size, a big small if you like as far as size....


Another example, an adult male rat with his male offspring who is a small in these photo's (smaller than that black female rat pictured above)...


Here is a link to www.rodentpro.com Check them for exact lengths and weights on each developmental stage of both mice and rats.

Here's a handy comparison size chart for mice and rats....