This online kettlebell rep calculator allows you to calculate your 1 rep max if you don’t know it. For example, you might not have heavier weight available but you know that with the heaviest weight you have, you can perform 3, 5, or x reps. Put that value in the box and click calculate.
A real-world example: Joe’s heaviest kettlebell is 56 lbs and he can complete 4 reps max with that. To find out what his 1RM would be, he would select 4RM from the dropdown and enter 56 in the text field, click calculate and have all values from 1RM to 12RM calculated.