Comparable Squier and Fender instruments are the same or very similar in size, depending on the specific guitar or bass. Fender guitars have a scale length of 25.5 inches, and their basses a scale length of 34 inches. Squier is the same.
However, both brands have smaller instruments in their lineups, such as the Squier Bronco bass which has a scale length of 30 inches, and the Fender Jaguar guitar which has a scale length of 24 inches.
Body sizes and styles will vary slightly, not only between Squier and Fender, but also between Fender instruments from different eras. These differences are incredibly subtle. Neck shapes vary. The weights of the instruments vary, depending on the wood used and the routing of the guitar, and the contours of the body may differ slightly when comparing different eras.
For the average beginner who is interested in a Squier, none of this should be of concern. A Squier made today is designed to be an affordable alternative to Fender, and so will be almost identical at first glance.