Question: what is the difference between the small and large fitbit alta hr?
Answer: Basically, Small fits 5.5"-6.7" (140mm-170mm) wrists. Large will fit those who are 6.7"-8.1" (170mm-206mm). X Large is for those with wrists that are 8.1"-9.3" (206mm-236mm) in size. If you're reading this for answers, you'll probably fall under the Small size.