Rep Max Converter

The Epley formula underlying most rep max converters shows 2-5% error for trained athletes using 2-10 reps. Accuracy decreases significantly beyond 10 reps. Research from the Journal of Strength and Conditioning Research confirms these conversions are most reliable for compound movements like squat, bench, and deadlift. Use converted values as starting points and adjust based on actual performance.

Traditional charts (like Prilepin's) are based on averages across populations, while formula-based conversions calculate individual estimates. The Epley formula predicts 10RM equals approximately 75% of 1RM, while some charts show 70-73%. Individual muscle fiber composition (fast vs. slow twitch dominant) causes these variations. Athletes with more fast-twitch fibers may find formula estimates too conservative for high-rep sets.

While mathematically possible, rep max formulas are validated primarily for multi-joint compound movements. Isolation exercises involve smaller muscle groups, different fatigue patterns, and technique variations that reduce accuracy. Research shows the highest prediction accuracy for bench press, squat, and deadlift. For exercises like bicep curls or leg extensions, treat conversions as rough estimates only.

Rep max tables enable undulating periodization by showing equivalent loads across rep ranges. For example, switching from 5x5 to 3x8 while maintaining relative intensity requires adjusting weight based on the conversion table. The NSCA recommends this approach for intermediate and advanced lifters. Use the table to plan mesocycle progressions: start with higher reps at lower percentages, progressing to lower reps at higher percentages.

Several factors cause discrepancies: training history (endurance vs. strength emphasis), muscle fiber type distribution, exercise technique efficiency, psychological factors, and fatigue state. Athletes who train primarily in low rep ranges often underperform predictions at higher reps, and vice versa. Track actual performance and adjust expectations accordingly, as rep max equations may not reflect your current status.

Both are widely used 1RM prediction formulas but differ in their mathematical approach. The Epley formula (1RM = weight × (1 + reps/30)) tends to produce slightly higher estimates at higher rep ranges. The Brzycki formula (1RM = weight × 36/(37 - reps)) is considered more accurate for rep ranges of 1-10. Research shows both formulas produce similar results for 5 reps or fewer, with divergence increasing at higher rep counts. Most coaches recommend using whichever formula matches your actual tested performance more closely.