One Rep Max Calculator
Estimate your one rep max from any set using the Epley and Brzycki formulas.
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Mesostrength tracks your estimated 1RM over time and uses it to auto-program your training loads.
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Automatic weight and rep prescriptions every session.
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Built-in deload timing that prevents overtraining before it starts.
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Understanding Your One Rep Max
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It serves as the foundation for percentage-based training programs and helps you track long-term strength progress without maxing out frequently.
How the Formulas Work
This calculator uses two well-validated estimation formulas:
- Epley formula - 1RM = weight x (1 + reps / 30). Works best for moderate rep ranges (3-10 reps) and tends to give slightly higher estimates at higher rep counts.
- Brzycki formula - 1RM = weight x (36 / (37 - reps)). More conservative at higher reps and closely matches the Epley formula in the 1-6 rep range.
Both formulas become less accurate beyond 10 reps. For the most reliable estimate, use a weight you can lift for 3-6 reps.
Why RPE Improves Accuracy
When you provide an RPE rating, the calculator accounts for reps in reserve (RIR). A set of 5 reps at RPE 8 means you had 2 more reps left, so your effective rep count is 7. This adjustment gives a more accurate estimate than assuming every set goes to failure.
Using Your 1RM in Training
Most programs prescribe loads as a percentage of 1RM. Typical guidelines include 70-85% for hypertrophy work (6-12 reps) and 85-95% for strength work (1-5 reps). The percentage table above gives you ready-to-use weights for each training zone. Recalculate every 4-6 weeks as your strength changes.
Frequently Asked Questions
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