Rat terriers are longer legged and are more lean of a breed than the jack russell the coat on the rat is softer and shorter usually and they are way less hyper of a breed.
Well, I'm not completely sure but my understanding is that jack russell terriers have floppier ears and a heavier build while rat terriers are smaller and their ears stand up. I'm really trying to differentiate between the rat terrier and the jack rat terrier as I am trying to find out how to tell the difference in them.
Jack Russells are white with orange splotches. (As a general rule). Rat terriers are more of a wider variety of color patterns, white with black splotches, for one. Jack Russells tend to be quite jumpy, and may be aggressive towards humans, whereas Rat Terriers are calmer. The world record for most rats kil;led by a single dog in one day goes to a rat terrier back in the early 20th century in a barn in North America. Something like 2,000 rats in an 8 hour period. That must have been one tired dog after that fact!
Well my dog is a jackrat terrier he has every thing a jackrussell has but he has the body of a jack but he got his hyper part from the jackrussell but he has a little bit of a calm side of a RAT TERRIER. So the diff is that a rat terrier has less active problems and the jack is a dog that feels like the big dog so its more alert but has a hyper problem. But the jackrussell is a dog that tends to be outdoors and look for animal and burn off some steam so be sure to let it go out side more to let some steam off and the same for the rat but some have diff attitudes and more can act differently.