One Rep Max (1RM) Calculator

Understanding Your One-Rep Max (1RM)

Your one-rep max is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength and serves as the foundation for percentage-based training programs used by powerlifters, strength coaches, and recreational athletes alike.

How 1RM Formulas Work

Directly testing your 1RM requires a spotter, proper warm-up, and carries some injury risk — especially for beginners. Estimation formulas let you predict your max from a submaximal set. This calculator uses three widely validated formulas:

• Epley (1985): One of the most popular formulas, calculated as weight × (1 + reps/30). It tends to be slightly more accurate for higher rep ranges (6–10).
• Brzycki (1993): Uses the formula weight × 36/(37 − reps). It is often considered more accurate for lower rep ranges (2–5) and is widely used in collegiate strength programs.
• Lombardi: Calculated as weight × reps^0.10. This formula produces slightly more conservative estimates and works well across a broad range of rep counts.

For the most accurate estimate, use a weight you can lift for 3–6 reps. Predictions become less reliable beyond 10 reps because muscular endurance begins to influence the result more than maximal strength.

Training with Percentages of Your 1RM

Once you know your estimated 1RM, you can program your training with precise intensity targets. Different percentage ranges produce different adaptations:

• Strength (85–100%): Heavy loads with low reps (1–6) maximize neural drive and maximal force production. This range is the bread and butter of powerlifting programs and peaking phases.
• Hypertrophy (67–85%): Moderate loads with moderate reps (6–12) optimize the mechanical tension and metabolic stress that drive muscle growth. Most bodybuilding and general fitness programs spend the majority of training time here.
• Endurance (50–67%): Lighter loads with higher reps (15–30) build muscular endurance, improve work capacity, and can serve as effective deload or recovery work.

Progressive Overload and Retesting

Progressive overload — gradually increasing the demands placed on your muscles — is the fundamental driver of strength and muscle gains. You can achieve this by adding weight to the bar, performing more reps at the same weight, adding sets, or decreasing rest periods. As you get stronger, your 1RM will increase, so it is important to re-estimate every 4–8 weeks to keep your training percentages accurate and your progress on track.

Safety Tips for 1RM Testing

If you choose to test your actual 1RM rather than estimate it, follow these guidelines: warm up thoroughly with progressively heavier sets, always use a competent spotter or safety pins, maintain strict form throughout the lift, and avoid testing when fatigued or under-recovered. For most lifters, estimating from a 3–5 rep set is safer and nearly as accurate as a true max attempt.