What Is a One-Rep Max Calculator?
A one-rep max (1RM) calculator estimates the heaviest weight you could lift for a single repetition, based on a weight and rep count you've actually performed — useful for programming training percentages without needing to test a true max lift.
How to Use the One-Rep Max Calculator
- Enter the weight you lifted.
- Enter how many reps you completed with that weight.
- View your estimated 1RM and suggested training percentages.
One-Rep Max Formulas
Both formulas are widely used estimates; they tend to agree closely for lower rep counts (under about 10) and diverge more at higher rep ranges, where estimation becomes less reliable.
Worked Example
Epley: 185 × (1 + 5÷30) = 185 × 1.1667 ≈ 216 lb
Brzycki: 185 × 36 ÷ (37−5) = 185 × 36 ÷ 32 ≈ 208 lb
Understanding Your Results
Estimated 1RM gives you a target for programming. Training Percentages translate that estimate into practical working weights for different rep ranges and training goals — lower reps at higher percentages build strength, while higher reps at lower percentages target hypertrophy and endurance.
Tips for Using 1RM Estimates
- Estimates are most accurate for sets of 10 reps or fewer — higher rep sets introduce more estimation error.
- Use estimated 1RM to plan percentage-based training, not necessarily to attempt an actual max lift, which carries higher injury risk without proper preparation.
- Recalculate periodically as strength changes with training.
Common Mistakes to Avoid
- Treating the estimate as an exact number rather than a useful approximation.
- Using very high rep sets (15+) for estimation, which tends to be less accurate.
- Attempting an actual 1RM test without proper warm-up, form, and (ideally) a spotter.
Frequently Asked Questions
It's the maximum weight a person can lift for a single, complete repetition of an exercise with good form.
They're reasonably accurate for lower rep ranges (under about 10 reps) but become less reliable at higher rep counts, since fatigue and endurance play a larger role.
The Epley and Brzycki formulas are both widely used and tend to produce similar results for common rep ranges — neither is definitively "more correct," and averaging both can be a reasonable approach.
Many lifters use estimated 1RM for programming rather than testing directly, since true max attempts carry higher injury risk and require significant warm-up, technique, and often a spotter.
Recalculating every few weeks or after a strength block can help keep training percentages accurate as your strength changes.