One-Rep Max Calculator (1RM) — Epley, Brzycki, Lombardi
Quick Answer
One-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form; a trained lifter's 1RM is typically 1.33 times their 10-rep weight using the Epley formula. The National Strength and Conditioning Association (NSCA) recommends 2–5 rep tests for safety when estimating 1RM rather than attempting a true maximum.
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Estimated 1RM
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Training percentages
| 95% (2–3 reps) | — |
| 90% (3–4 reps) | — |
| 85% (5 reps) | — |
| 80% (6–8 reps) | — |
| 75% (8–10 reps) | — |
| 70% (10–12 reps) | — |
| 60% (12–15 reps) | — |
| 50% (warm-up) | — |
How 1RM Estimation Works
A one-rep max (1RM) is the heaviest weight you can move for a single complete repetition of a lift. Rather than testing 1RM directly — which is stressful, risky, and impractical in most training sessions — strength coaches use regression equations to predict 1RM from a sub-maximal set. The lifter performs as many reps as possible with a moderate weight, and the formula converts weight × reps into a projected single-rep ceiling. The National Strength and Conditioning Association (NSCA) and the American College of Sports Medicine both endorse rep-max estimation as the primary way to prescribe training loads in its Essentials of Strength Training and Conditioning textbook.
Accuracy depends on the formula and the rep range. Research in the Journal of Strength and Conditioning Research has shown that all popular formulas are most accurate in the 2–10 rep range; beyond 10 reps, errors can exceed 10% because muscle endurance becomes the limiting factor instead of pure strength. This calculator implements seven of the most-cited formulas — Epley, Brzycki, Lombardi, Mayhew, Wathan, and O'Conner — plus an average option. Once you have an estimated 1RM, you can build a complete program using percentage-of-1RM prescriptions, which are the standard for periodized training. See also our body fat calculator and macro calculator.
The Six 1RM Formulas
Epley (1985): 1RM = w × (1 + r ÷ 30). Brzycki (1993): 1RM = w × 36 ÷ (37 − r). Lombardi (1989): 1RM = w × r^0.10. Mayhew et al. (1992): 1RM = 100w ÷ (52.2 + 41.9 × e^(−0.055r)). Wathan (1994): 1RM = 100w ÷ (48.8 + 53.8 × e^(−0.075r)). O'Conner (1989): 1RM = w × (1 + 0.025r). Worked example: 225 lb for 5 reps by Epley gives 225 × (1 + 5 ÷ 30) = 225 × 1.1667 ≈ 263 lb. Brzycki gives 225 × 36 ÷ 32 ≈ 253 lb. Lombardi gives 225 × 5^0.10 ≈ 262 lb. The three cluster around 253–263 lb, a reasonable band within which the true 1RM should lie.
Key Terms You Should Know
1RM: the maximum weight liftable for one repetition. RM: "rep max" — e.g., 5RM is the weight you can lift for exactly 5 reps before failure. Submaximal: any weight below your 1RM, typically described as a percentage. AMRAP: "as many reps as possible," a test set used to estimate 1RM from a submaximal weight. RPE: rate of perceived exertion, a 1–10 self-rating scale often used alongside percentage training. Periodization: the planned variation of intensity and volume across weeks or months to maximize long-term gains.
Rep-to-1RM Conversion — Reference Data
The table below shows the percentage of 1RM corresponding to each rep target, based on an average of the Epley and Brzycki formulas — the same table published in the NSCA Essentials textbook. Use it to convert test sets into 1RM or to plan training loads once you know your estimated 1RM.
| Reps | % of 1RM | Primary Adaptation |
|---|---|---|
| 1 | 100% | Maximal strength (test) |
| 2 | 95% | Maximal strength |
| 3 | 93% | Maximal strength |
| 5 | 87% | Strength |
| 6 | 85% | Strength |
| 8 | 80% | Strength / hypertrophy |
| 10 | 75% | Hypertrophy |
| 12 | 70% | Hypertrophy |
| 15 | 65% | Endurance / hypertrophy |
Practical Examples
Example 1 — Bench press. A lifter benches 185 lb for 8 reps. Epley: 185 × (1 + 8 ÷ 30) = 234 lb. Brzycki: 185 × 36 ÷ 29 ≈ 230 lb. Estimated 1RM is about 230–234 lb. Example 2 — Squat cycle. With a 315 lb estimated 1RM, a 5×5 program at 80% would be 315 × 0.80 = 252 lb, rounded down to 250 lb on the bar. Example 3 — Deadlift peak. After 8 weeks of training, a lifter moves from 315 lb × 5 reps (1RM ≈ 368) to 335 lb × 5 reps (1RM ≈ 391) — a 23 lb, 6% strength gain, typical of an intermediate trainee per published NSCA progression guidelines.
Tips and Best Practices
Test within the 2–5 rep range. Formulas are most accurate at low reps; tests above 10 reps are unreliable. Warm up thoroughly. The NSCA protocol calls for 5–10 easy reps, then progressively heavier sets of 3–5 reps before the test set. Rest 3–5 minutes between heavy sets. Full ATP-PCr recovery allows near-maximum force output. Compare formulas. Using the average of two or three reduces the effect of any single formula's bias. Reassess every 8–12 weeks. True strength gains are slow; testing more often risks measuring day-to-day fluctuation instead of progress. Always lift with safety equipment. A power rack, spotter, or competition-grade safeties are essential when approaching 1RM.
Frequently Asked Questions
What is a one-rep max?
A one-rep max, or 1RM, is the maximum weight you can lift for a single repetition of an exercise with proper form. It is the gold standard for measuring maximal strength and is used to prescribe training intensities as a percentage of 1RM. The National Strength and Conditioning Association (NSCA) defines 1RM testing protocols in its Essentials of Strength Training and Conditioning textbook, and recommends warm-up sets before any maximum attempt.
Which 1RM formula is most accurate?
Research published in the Journal of Strength and Conditioning Research shows that no single formula is universally most accurate, and accuracy drops sharply above 10 reps. The Brzycki formula tends to be most accurate for reps of 2 to 10, while the Epley formula is the most widely used in popular training software. Mayhew and Wathan equations are often more accurate for bench press, and O'Conner for squats. This calculator shows all seven so you can average them.
How many reps should I use to estimate my 1RM?
The NSCA recommends using a set of 2 to 5 repetitions performed to near-failure, because formula error grows quickly above 10 reps. A 5-rep test is the most common compromise between safety and accuracy, and is the protocol used in the NSCA Certified Personal Trainer handbook. If you can do more than 10 reps, the weight is too light and the estimate will be unreliable. For safety, always warm up and lift in a power rack with a spotter.
What is the Epley formula?
The Epley formula, published by Boyd Epley in 1985, estimates 1RM as weight × (1 + reps ÷ 30). For example, lifting 225 lb for 5 reps gives 225 × (1 + 5 ÷ 30) = 225 × 1.167 = 262.5 lb estimated 1RM. Epley designed the formula for use in the University of Nebraska strength program and it has since become the default equation in most commercial gym software.
How often should I max out?
Most strength coaches recommend testing 1RM no more than every 8 to 12 weeks, typically at the end of a training cycle. True maximum lifts are stressful to the central nervous system and carry a higher injury risk than submaximal work. Between tests, use a rep-max calculator like this one to track progress safely. The NSCA and USA Weightlifting both emphasize that estimated 1RMs are sufficient for most program design, and real maxes should be reserved for competition or key benchmarks.
What percentage of 1RM should I train at?
Training intensity depends on the goal. For maximal strength, lift at 85 to 100 percent of 1RM for 1 to 5 reps. For hypertrophy (muscle growth), work at 65 to 85 percent for 6 to 12 reps. For muscular endurance, lift 50 to 65 percent for 15 or more reps. These ranges come from the ACSM's Guidelines for Exercise Testing and Prescription and the NSCA Essentials textbook, both widely used in coaching certification programs.