One Rep Max Calculator
Percentage Chart
| Reps | % of 1RM | Estimated Weight |
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About One Rep Max Calculator
What Is One Rep Max?
One Rep Max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the gold standard measure of maximal strength and serves as the foundation for programming training loads. Most well-designed strength programs prescribe weights as a percentage of your 1RM (for example, 5 sets of 5 at 80% 1RM). However, actually testing your true 1RM is physically demanding and carries injury risk, which is why calculated estimates from submaximal efforts are so valuable.
1RM Estimation Formulas
This calculator uses three validated formulas: Epley: 1RM = weight x (1 + reps/30), Brzycki: 1RM = weight x (36 / (37 - reps)), and Lombardi: 1RM = weight x reps^0.1. These formulas are most accurate when using 3-10 repetitions. Above 10 reps, accuracy decreases. The Epley and Brzycki formulas are the most widely used and produce nearly identical results for rep ranges under 10.
How to Use This Calculator
Enter the weight you lifted and the number of reps you completed (with good form, not grinding failure reps). The calculator estimates your 1RM and provides a percentage chart showing how much weight to use for different rep ranges: 95% for 2 reps, 90% for 4 reps, 85% for 6 reps, 80% for 8 reps, 75% for 10 reps, and so on. This chart becomes your training reference.
Frequently Asked Questions
How accurate are 1RM estimates?
Very accurate when using 3-6 reps (within 5% for most people). Accuracy decreases with higher rep sets because fatigue, cardiovascular fitness, and mental factors play a larger role. Always use your best recent set.
Should I actually test my 1RM?
Testing is optional. Calculated estimates are sufficient for programming. If you do test, warm up thoroughly, use a spotter, and attempt no more than 3-5 maximal singles. Test only when fresh and recovered, not after a hard training week.
How often should I update my 1RM?
Recalculate every 4-8 weeks or whenever you hit a new rep PR at a given weight. Beginners should update more frequently as strength gains come rapidly in the first year of training.
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