What is one rep max (1RM)?
One rep max (1RM) is the maximum amount of weight a person can lift for a single repetition of a given exercise. It is one of the most important strength training metrics, used for planning training intensity and tracking progress over time.
How to calculate one rep max?
You can estimate your 1RM indirectly by lifting a weight you can handle for multiple repetitions (2–10 reps) and applying a mathematical formula. This calculator uses five well-established formulas: Epley, Brzycki, Lander, Lombardi, and O'Conner, then averages them for a more reliable estimate.
What are the 1RM formulas?
- Epley: 1RM = weight × (1 + reps / 30)
- Brzycki: 1RM = weight × 36 / (37 − reps)
- Lander: 1RM = weight × 100 / (101.3 − 2.67123 × reps)
- Lombardi: 1RM = weight × reps^0.10
- O'Conner: 1RM = weight × (1 + reps / 40)
One rep max calculation examples
If you can squat 80 kg for 8 reps, the Epley formula gives: 80 × (1 + 8/30) = 101.3 kg. The Brzycki formula yields: 80 × 36 / (37 − 8) = 99.3 kg. Averaging all five formulas provides the most reliable estimate of your true 1RM.
How to use your 1RM for training?
Training programs are often prescribed as percentages of your 1RM. For strength development, use 85–95% of 1RM with 1–5 reps. For muscle hypertrophy, use 65–80% with 6–12 reps. For muscular endurance, use 50–65% with 15–20+ reps.
When are 1RM calculations most accurate?
The formulas are most accurate when the number of repetitions is between 2 and 10. Beyond 10 reps, estimates become less reliable because muscular endurance plays a larger role than maximal strength.