I have been lifting regularly for about 5 or so years, and I've never really given much thought to wearing a belt. Compared to the majority of this site I'm probably not considered strong, but I am finding a bunch of back issues lately after squatting heavy (heavy for me, that is) and deadlifting. I threw a belt on during deadlifting yesterday (just a BS belt they had there) and it seemed to help but I kept blowing the damn thing open (just a velcro strap). I want to invest in a quality piece, something that won't come open on me half way through a pull. I've done some research and it seems like a 10mm will be good for me. What confuses me slightly is the size. I'd say right now my waist is about 36, and my weight fluctuates considerable. I tend to diet throughout the year and right now I have a pregnant girlfriend so dieting is just impossible (she eats EVERYTHING!). So I'm probably going to bulk for the next few months, so my waist can jump to about 38 or so, then down to around 32-34 when I decid to diet. Is there a recommended belt that'll grow-shrink with me?
First off make sure you are measuring around your belly where you will wear the belt. I have two inzer 13mm lever belts. I have a large which I bought when I was about 36" and it fit all the way up to 42" plus and fit smaller than the 36" easily, I also bought a XXL belt recently and measured something like 45" and I've still got tons of room to get bigger although i don't plan to. I imagine I will be back in the large by later this year if I stick to my goals. Inzer has a size chart, but there are plenty of holes in the belt to exceed each direction, also you can return it within I think 2 weeks and get a different size. Something to think about, but they aren't the only option, plenty of choices out there.
Keep in mind if you are having pain squatting and deadlifting you don't want to band aid it with a belt to cover up the pain. You should figure out what you are doing wrong and correct it.
A belt should help create better trunk/core stability. So if that helped with the pain, is that saying something about your core? Or maybe the feel of the belt helped you keep better position and hence didn't overextend or overflex the lower back when deadlifting or squatting.
Inzer makes a sturdy belt. Others are fan's of Best Belts.
I'm no expert. I tend to fumble my way through this stuff. I might actually make progress if I start learning the right way to do this shit!