The average Chihuahua is about 3 to 6 pounds and about 8.5 to 13 inches tall, while the Jack Russell can weigh anywhere from 13 to 17 pounds and be 10 inches to 15 inches tall. So predicting exactly what a Jackchi pup will look like is definitely a guessing game. With that said, however, most Jack Russel Chihuahua mixes will look somewhat alike.