Photo courtesy of Coach Ron Jones, KBLA RKC
If you've decided to start training with kettlebells and devote time to experiencing the improvements that they can offer you, you'll need to actually get your hands on some kettlebells! BUT WHICH ONES?!?
Here's my personal guideline.
Because the most fundamental exercises in kettlebell training are the Swing & the Turkish Get-Up, I strongly suggest having two different kettlebells. If you're thinking that having to shell out the money for two kettlebells is expensive, let me tell you that coming to see a doctor or therapist after you injure yourself trying to be a badarse with horribly compensated technique is much more expensive.
Invest on the front end, reap on the back end. Skimp on the front end, pay terribly on the back end.
The lighter kettlebell will allow you to learn the Turkish Get-Up with a weight that should allow you to be challenged safely without being too stressed to pay attention to good form. It will also allow you to make tweaks to your Swing form without great risk of injury to yourself.
Men - You'll ideally need both a 12kg (26lb) kettlebell and a 20kg (44lb) kettlebell. I know, I know, I know... You bench press with 5 plates on each side & can squat with a buffalo on your back. I don't care. The Swing & Turkish Get-Up CAN be done as strength movements, but finesse and technique are primary concerns in the RKC method - NOT brute strength. Remember that every point of technique you overlook will come back to haunt you eventually. Trust me on that.
Now if you're one of those folks who's ridiculously strong, coordinated, and un-injured, you can certainly err towards the larger sized kettlebells. As long as you can maintain correct form on BOTH sides for Pavel's Program Minimum, which I believe he goes over in Enter the Kettlebell, use whatever sized bell you want. Remember that the sizes I mentioned in this post are nothing more than general guidelines for the average male & female based on my experiences in teaching around the world.
Remember, too, that NOTHING takes the place of working on the above exercises with a skilled instructor, not just a skilled athlete!