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One Rep Max Calculator
Calculate your maximum strength (1RM) for any lift. Predict your one-rep max based on your current lifting performance to safely plan your training.
Your Lift
Understanding One Rep Max (1RM)
Your One Rep Max is the theoretical maximum weight you can lift for a single repetition. Knowing this number is crucial for designing effective strength training programs based on percentage-based training.
Why Use a Calculator?
Testing a true 1RM involves lifting heavy loads to failure, which carries a risk of injury and significant central nervous system fatigue. Using a calculator allows you to estimate your max safely based on sub-maximal lifts (e.g., lifting a weight for 3-5 reps).
Training Percentages
- Strength: 85-100% of 1RM (1-5 reps)
- Hypertrophy (Muscle Growth): 70-85% of 1RM (6-12 reps)
- Endurance: Below 70% of 1RM (12+ reps)
⚠️ Safety Warning
Never attempt a true 1RM test without a spotter and proper warm-up. This calculator uses the Epley formula, which is most accurate for rep ranges between 1 and 10.
💡 Expert Tip from Dr. Alex M.
For the most accurate estimate, use a weight you can lift for 3-5 reps. Higher rep sets (like 15-20 reps) are less reliable for predicting maximum strength due to the endurance factor.
Frequently Asked Questions
What is a One Rep Max (1RM)?
Your One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is considered the gold standard for measuring absolute strength.
Is the 1RM calculator accurate?
1RM calculators provide a close estimate, especially if the number of repetitions used for the calculation is low (under 10). The accuracy decreases as the number of reps increases.
How often should I test my 1RM?
Testing your true 1RM places significant stress on the body. It is generally recommended to test it every 8-12 weeks, or simply use a calculator to estimate it based on your working sets to avoid injury risk.