One Rep Max Calculator

What Is One Rep Max (1RM)?

One rep max, or 1RM, is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring maximal strength and is used by strength coaches, personal trainers, and athletes worldwide to design training programs. Knowing your 1RM allows you to calculate the exact weight you should use for any given rep range, ensuring your training is precisely calibrated for your goals whether that is strength, hypertrophy, power, or endurance.

Understanding the Four Formulas

The Epley formula (1985) is the most widely used 1RM prediction equation. It tends to produce slightly higher estimates and works well for moderate rep ranges (3 to 10). The Brzycki formula (1993) is popular in academic research and produces nearly identical results to Epley for low reps but diverges for higher rep ranges. The Lombardi formula uses an exponential approach and is often considered more conservative. The O'Conner formula uses a simple linear model and tends to produce the lowest estimates.

Which Formula Is Most Accurate?

Research suggests that no single formula is universally superior. The Epley and Brzycki formulas are most accurate for 1 to 6 repetitions. All formulas lose accuracy above 10 reps because high-rep sets introduce muscular endurance as a confounding variable. For best results, test with a weight you can lift for 3 to 5 reps. This calculator shows all four results plus an average, giving you a reliable range rather than a single potentially misleading number.

Training Weight Percentages

Once you know your 1RM, you can calculate training weights for any goal. Strength training (1 to 5 reps) uses 85 to 100% of 1RM. Hypertrophy training (6 to 12 reps) uses 67 to 85%. Muscular endurance (13 to 20+ reps) uses 50 to 67%. Power training uses 50 to 70% with explosive movement. These percentages are guidelines; individual variation means some athletes may handle slightly more or less weight for a given rep range.

How to Test Safely

Never attempt a true 1RM test without a spotter and proper warm-up. Start with 2 to 3 sets at 50 to 70% of your estimated max, then work up in small increments (5 to 10% jumps). Allow 3 to 5 minutes of rest between heavy attempts. Using this calculator with a submaximal set (3 to 5 reps) is safer and nearly as accurate as testing a true single. Always prioritize form over weight, as the risk of injury increases exponentially at maximal loads.

Progressive Overload and 1RM

Retest or recalculate your 1RM every 4 to 8 weeks to ensure your training weights keep pace with your strength gains. Progressive overload, the gradual increase of training stress, is the fundamental principle of strength development. If your training weights remain the same for months, your body has no stimulus to adapt and grow stronger. Tracking your estimated 1RM over time is one of the clearest indicators of strength progress.

1RM Across Different Exercises

Your 1RM varies enormously between exercises. A 100 kg squat and a 100 kg bench press represent very different levels of strength because the muscles involved, range of motion, and leverage differ. Common strength standards for intermediate male lifters (as ratios of body weight) are: Bench Press 1.0-1.5x, Squat 1.25-2.0x, Deadlift 1.5-2.5x, Overhead Press 0.65-1.0x. Female lifters typically achieve 60 to 75% of these ratios. Use this calculator separately for each exercise in your program.