1RM calculator
Type your max and pick a percentage: the weight comes out rounded down to your plates, with the plates for each side of the bar.
Calculator
Percentage
Epley
Brzycki
Estimates: less reliable above 10 reps.
How it works
The working weight is your max times the percentage, rounded down to the smallest jump your plates allow: 2.5 kg with 1.25 kg plates, or 5 lb with 2.5 lb plates. Rounding down means never loading more than was programmed.
The estimated max uses the Epley and Brzycki formulas. They are estimates: the more reps, the less reliable, and above 10 it is better not to use them.