Free 1RM Calculator — One Rep Max & Strength Percentages
Enter a weight and rep count to estimate your one rep max using the Epley and Brzycki formulas. Get a full percentage chart for setting training weights. Free, no signup required.
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Get Protokl →How to Use 1RM Percentages for Program Design
Training at specific percentages of your 1RM is how evidence-based strength programs target different physiological adaptations. Each intensity zone drives a different response:
| Zone | % of 1RM | Rep Range | Adaptation |
|---|---|---|---|
| Max Strength | 90–100% | 1–3 | Neural efficiency, peak strength |
| Strength | 80–90% | 3–5 | Strength + some hypertrophy |
| Hypertrophy | 65–80% | 6–12 | Muscle growth (primary zone) |
| Power / Speed | 55–75% | 1–5 (explosive) | Rate of force development |
| Endurance | 50–65% | 15+ | Metabolic conditioning, work capacity |
Most intermediate and advanced programs cycle through multiple zones within a week (daily undulating periodization) or across a training block (linear / block periodization). Re-test your 1RM estimate every 4–8 weeks as your strength increases to keep working weights accurate.
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Frequently Asked Questions
How is one rep max calculated?
This calculator averages two formulas: the Epley formula (weight × (1 + reps / 30)) and the Brzycki formula (weight × 36 / (37 − reps)). Averaging the two improves accuracy across a range of rep counts. The formulas are most accurate for sets of 1–10 reps — predictions become less reliable above 12 reps because fatigue and technique play a larger role.
Should I actually attempt my calculated 1RM?
Not necessarily. The calculated 1RM is a training tool for program design, not a target to hit every session. True max singles carry injury risk and require specific peaking. Most lifters are better served using the percentage chart to set working weights — for example, sets of 5 at 80–85% or sets of 3 at 87–92%. Test your actual 1RM only during a dedicated peaking cycle.
What percentage of 1RM should I use for different training goals?
Strength (1–3 reps) is trained at 90–100% of 1RM. Power and speed-strength work is done at 55–75% with maximal bar speed. Hypertrophy (muscle growth) is most efficiently trained at 65–85%, corresponding to sets of 6–15 reps. Muscular endurance work uses 50–65% for 15+ reps. Most programs cycle through multiple zones across a week or training block.
Why does my actual 1RM differ from the calculator?
Formula-based 1RM estimates assume consistent technique and full-effort sets, which rarely hold perfectly in practice. Individual fiber type distribution also affects how well estimates generalize — fast-twitch dominant lifters tend to hit higher actual maxes than the formula predicts. Use the calculator as a close starting point and adjust your working weights based on how sets actually feel in training.