The best kettlebell size for you is one that feels manageable enough to lift but heavy enough that your muscles feel exhausted during the last few reps of each set.
Our kettlebells come in the standard sizes. You'll get a good idea of what weight works for you by doing 3 sets of 10 reps for a few different exercises. Note down which weights you're capable of doing. We recommend the JTX 6KG Kettlebell if you haven't done any weight training before. Start small, then work your way up in weight. As you progress in weight, you'll find that the heavier kettlebells and the lighter kettlebells suit different exercises. For instance you may use a lighter kettlebell to perform a kettlebell halo, but for a kettlebell squat you'll want a heavier variant. Generally, the larger the muscle group you are working, the heavier the kettlebell you'll want to use.
If you're looking to buy kettlebells to strengthen and build your muscles, we recommend investing in a set. With only one kettlebell you'll be able to strengthen and build your muscles to an extent that will be enough for most people. You can do this by increasing the number of reps, or sets, you perform over time. However, there will come a time where your kettlebell doesn't exhaust your muscles anymore. At this point, your exercises will be toning, but not building muscle. With multiple kettlebells you'll be able to move up a weight when you're ready or swap to lower weights for weight training weaker areas of your body.