You'll find that different weights will be needed for different exercises. For example, I curl 25's. I can press 20's. I can do tricep extensions with 20's. But for shoulders? So weak. On lateral extensions (where you raise the dumbbells from your hips to shoulder height holding your arms out sideways) I can only do about 5 lbs in each hand. And if you're doing a program that focuses on lots of reps, the weight you can do goes down as your reps go up. A set that goes up to 25 lbs would probably be good for quite a while. I got a set of those Bowflex Selectechs this year and love them- one set of dumbbells replaces them all.