Rating

I'm interested in purchasing carabiners for climbing purposes, how do they rate them, and is there a way of figuring how much weight each has by the numbers stamped on them?

Carabiners are usually rated in kilonewtons (kN). 1kN=224.8 lbs. The kN rating should be stamped on the spine of the carabiner. The accepted standard for life support in most climbing circles is 22kN and above. I would also recommend that you get double locking/triple actions carabiners as those are less likely to pop open unexpectedly.