1 Rep Max Calculator
Estimate your peak strength without the risk of heavy singles.
Based on the Epley Formula
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What is a 1 Rep Max (1RM)?
Your one-repetition maximum (1RM) is the heaviest weight you can lift for a single repetition of a specific exercise with proper form. It is the gold standard for measuring absolute strength in powerlifting, weightlifting, and general strength training. Knowing your 1RM is essential for designing effective training programs, as most percentage-based routines (like 5/3/1 or Starting Strength) rely on this number to determine your daily training loads.
How This Calculator Works
This tool uses the Epley Formula, which is widely considered one of the most accurate mathematical models for predicting strength. The formula is expressed as:
1RM = Weight × (1 + 0.0333 × Reps)
While testing a true 1RM can be taxing on the central nervous system and carries a higher risk of injury, using a sub-maximal load (a weight you can lift for 3–8 reps) and calculating the 1RM is a safer and more practical alternative for most athletes.
If you can bench press 185 lbs for 5 repetitions:
1RM = 185 × (1 + 0.0333 × 5)
1RM = 185 × 1.1665
Estimated 1RM = 215.8 lbs
Understanding Training Intensity
Once you have your 1RM, you can calculate specific training zones:
- 90-100% (Power): Used for peak strength and neurological adaptation. Usually 1-3 reps.
- 75-85% (Hypertrophy): The "sweet spot" for muscle growth. Usually 6-12 reps.
- 60-70% (Endurance/Form): Ideal for technical work, recovery sessions, or building muscular endurance.
Safety Tips for Heavy Lifting
Whether you are testing your max or lifting heavy percentages, always follow these rules:
- Use a Spotter: Especially for movements like the bench press or squat.
- Warm Up Properly: Start with an empty bar and gradually increase weight over 3-5 sets.
- Check Your Form: A 1RM "grind" should still maintain safe structural integrity. If your back rounds or knees cave excessively, stop the set.
- Rest: Allow 3-5 minutes of rest between heavy attempts to ensure ATP stores are replenished.