01Formula
1RM = weight × (1 + min(reps, 12) / 30). A single is the weight itself. Most accurate in the 3–8 rep range; high-rep sets lean on endurance more than max strength.
02FAQ
How accurate is a 1RM calculator?
Close enough to program off for sets of 3 to 8 reps. Beyond that the set measures endurance more than max strength, so the estimate runs high — this one caps the rep count at 12 to keep it honest.
Which formula does this use?
Epley: weight × (1 + reps / 30), with reps capped at 12. A single returns the weight itself.
Should I test my true 1RM?
Rarely. A real max needs a spotter, fresh legs, and a peak, and it costs days of recovery. A hard set of 3 to 5 gives you the same number to program from.
How do I use percentages of my 1RM?
Strength work sits near 80–90%, hypertrophy near 65–80%. The table converts your estimate into a load for every step from 100% down to 50%.