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One Rep Max (1RM) Calculator

Estimate your maximum lift using 7 distinct formulas (Brzycki, Epley, etc.). Includes strength zones and percentage-based training tables.

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About

Determining the maximum weight a designated muscle group can lift for a single repetition is a cornerstone of periodized strength training. Testing a true 1RM places significant mechanical stress on tendons and ligaments, increasing injury risk for novice or intermediate athletes. This tool utilizes submaximal performance data - specifically lifts performed for 2 to 10 repetitions - to extrapolate a theoretical maximum. By aggregating results from seven established regression models, including Brzycki and Epley, the calculator mitigates the bias inherent in any single formula.

Accuracy in these estimates dictates the efficacy of training cycles. A program prescribing 85% intensity based on an inflated max leads to neural fatigue; conversely, underestimated values result in sub-optimal hypertrophic stimulus. This utility normalizes these values, providing a reliable baseline for calculating working sets.

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Formulas

The calculator employs the Brzycki Formula for its linearity in lower rep ranges:

1RM = w1.0278 − 0.0278r

And the Epley Formula for higher rep counts:

1RM = w(1 + r30)

Where w is the weight lifted and r is the number of repetitions performed.

Reference Data

Intensity Zone% of 1RMRep RangeTraining Effect
Neuromuscular Power90−100%1−3Maximal Force Production
Maximal Strength85−90%3−5Myofibrillar Hypertrophy
Strength-Endurance70−80%6−12Sarcoplasmic Hypertrophy
Endurance<65%15+Metabolic Conditioning

Frequently Asked Questions

Each formula is derived from regression analysis of specific population datasets (e.g., collegiate football players vs. untrained individuals). The Epley formula tends to be more accurate for higher rep ranges (8-12), while Brzycki and Lander are often preferred for lower rep ranges (2-5). Using an average of multiple formulas provides a more robust estimate across different physiology types.
No. The formulas are coefficient-based ratios. Whether you input kilograms or pounds, the numeric relationship between the weight lifted and the repetitions performed remains constant. The output will reflect the input unit.
The accuracy of 1RM prediction equations degrades significantly beyond 10 repetitions. At higher rep ranges, metabolic fatigue (lactic acid accumulation) becomes a limiting factor before true neuromuscular failure, skewing the strength projection.
Recalculation is recommended at the end of a mesocycle, typically every 4 to 6 weeks. This ensures that your training percentages remain aligned with your current adaptation levels without the need for frequent maximal testing.