What 1RM is
1RM (one-rep max) is the maximum weight you can lift for a single complete repetition with correct form. Since testing this in practice is risky and exhausting (especially for beginners), the safer way is to estimate 1RM from a smaller number of reps performed with a submaximal weight — that's where this calculator comes in.
The formulas used
We combine two formulas widely used in strength training: Epley (1RM = weight × (1 + reps/30)) and Brzycki (1RM = weight × 36 / (37 − reps)) — both give similar results for low rep counts (up to 6-8), but tend to diverge more at higher rep counts, which is why we show the average of the two.
Percentage table
The load-by-percentage-of-1RM table is a classic training periodization tool: for example, pure strength training usually uses 85-100% of 1RM, hypertrophy usually uses 65-85%, and muscular endurance uses below 65%.
1RM estimates get less accurate above 10-12 reps — for those ranges, consider testing with fewer reps for a more reliable estimate. Always use correct form and, when possible, a training partner (spotter) for loads near your limit.
Frequently asked questions
Why two different formulas instead of just one?
No single estimation formula is perfect for everyone — showing Epley and Brzycki side by side, along with the average, gives a better sense of the likely range of your true 1RM than relying on one single number.
Can I use this for any exercise?
It works best for multi-joint, compound exercises (bench press, squat, deadlift), where form is more predictable — for isolation exercises (bicep curls, for example), the relationship between reps and max load tends to be less consistent.