Testing a true one-rep max is risky and time-consuming — most lifters estimate it instead from a lighter set taken close to failure. Our one-rep max calculator uses two well-established formulas to give you a realistic range rather than a single falsely-precise number.
The two formulas
Epley formula:
1RM = weight × (1 + reps / 30)Brzycki formula:
1RM = weight × 36 / (37 − reps)Example
135 lbs for 8 reps:
- Epley: 135 × (1 + 8/30) = 171.0 lbs
- Brzycki: 135 × 36/(37−8) = 167.6 lbs
Neither number is “the” correct answer — they’re both statistical estimates derived from population data, and real individual results vary based on training history, muscle fiber composition, and how close to true failure the set was taken.
Accuracy drops at higher rep counts
Both formulas are most reliable in the 1-10 rep range. Above 12-15 reps, the relationship between reps and percentage-of-max becomes less linear, and estimates get progressively less trustworthy — if you’re estimating from a 15+ rep set, treat the number as a rough guide only.
The percentage training table
Many strength programs prescribe working sets as a percentage of 1RM (“3×5 at 80%”). The calculator’s training table converts your estimated 1RM directly into the actual weight for each common percentage (50%-95%), saving the mental math before every session.
All calculations happen instantly in your browser as you adjust weight, reps, or unit (lbs/kg).