Health & Medicine · Fitness · Strength Training
Mayhew One Rep Max Calculator
Estimates your one-repetition maximum (1RM) from a submaximal lift using the Mayhew et al. (1992) exponential formula.
Calculator
Formula
W = weight lifted (kg or lb), R = number of repetitions performed to failure, e = Euler's number (~2.71828). The constants 0.522, 0.419, and 0.055 are empirically derived regression coefficients from the Mayhew et al. study.
Source: Mayhew, J.L., Ball, T.E., Arnold, M.D., & Bowen, J.C. (1992). Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research, 6(4), 200–206.
How it works
The Mayhew formula is: 1RM = W / (0.522 + 0.419 × e−0.055 × R), where W is the weight lifted and R is the number of repetitions completed to failure. The exponential term shrinks as reps increase, causing the denominator to approach 0.522 at very high rep counts and to approach 0.941 at a single rep — effectively calibrating the prediction for the full rep range.
Mayhew and colleagues derived these coefficients from muscular endurance tests on college athletes, making the formula particularly well-validated for trained individuals performing upper-body exercises such as the bench press. Compared to simpler linear models (e.g., Epley or Brzycki), the exponential curve more accurately models fatigue at higher rep counts.
Coaches use estimated 1RM values to assign percentage-based training loads (e.g., 75–85% for hypertrophy, 85–95% for maximal strength). The percentages output by this calculator (60%, 70%, 80%, 90%) correspond to the most commonly prescribed intensity zones in evidence-based programming.
Worked example
Example: An athlete bench-presses 85 kg for 10 repetitions to failure.
Step 1 – Calculate the exponent: −0.055 × 10 = −0.55
Step 2 – Evaluate e−0.55: e−0.55 ≈ 0.5769
Step 3 – Build the denominator: 0.522 + 0.419 × 0.5769 = 0.522 + 0.2417 = 0.7637
Step 4 – Divide: 85 / 0.7637 ≈ 111.3 kg
Training percentages: 90% = 100.2 kg | 80% = 89.0 kg | 70% = 77.9 kg | 60% = 66.8 kg
Limitations & notes
The Mayhew formula was validated primarily on college-aged athletes performing the bench press; accuracy may be lower for untrained individuals, older adults, or lower-body exercises such as the squat and deadlift. The formula assumes repetitions are taken to momentary muscular failure — partial sets will underestimate the true 1RM. Accuracy declines at very high rep counts (above 15–20 reps), where cumulative fatigue and cardiovascular limits distort the strength-endurance relationship. This tool provides an estimate only; always use appropriate spotters and progressive loading when approaching maximal lifts.
Frequently asked questions
How accurate is the Mayhew formula compared to other 1RM equations?
In the original Mayhew et al. (1992) study, the formula produced correlations of r = 0.97–0.99 with actual 1RM bench press values in college athletes. Independent comparisons (e.g., LeSuer et al., 1997) found the Mayhew equation slightly over-predicts at higher rep counts but is among the most accurate exponential models, particularly for the bench press in trained lifters.
Can I use this calculator in kilograms and pounds?
Yes. The formula is unit-agnostic — simply enter your weight in whichever unit you prefer (kg or lb). The estimated 1RM and all percentage outputs will be in the same unit. Do not mix units within a single calculation.
What is the ideal rep range for the most accurate Mayhew prediction?
The Mayhew formula is most accurate between 2 and 10 repetitions. As the rep count rises above 10–12, muscular endurance and cardiovascular factors play an increasing role, causing the predicted 1RM to become less reliable. For best results, choose a load you can lift for roughly 3–8 controlled reps to failure.
Is the Mayhew formula valid for exercises other than the bench press?
The formula was originally developed and validated for the bench press. It is frequently applied to other barbell lifts (squat, deadlift, overhead press), but independent validation is more limited for these movements. Exercise-specific regression equations may provide better accuracy for lower-body or machine exercises.
How do I use my estimated 1RM to set training weights?
Multiply your estimated 1RM by the desired training percentage. For example, if your 1RM is 100 kg: hypertrophy work (6–12 reps) typically uses 67–85% (67–85 kg); strength work (1–5 reps) uses 85–95% (85–95 kg); and technique or speed work uses 50–70% (50–70 kg). The percentage outputs provided by this calculator (60–90%) cover the most common programming zones.
Why does entering 1 rep not simply return the weight I entered?
At R = 1, the denominator equals 0.522 + 0.419 × e<sup>−0.055</sup> ≈ 0.522 + 0.419 × 0.9465 ≈ 0.9189, so the formula returns W / 0.9189 ≈ 1.088 × W. This slight upward adjustment reflects the statistical regression: a single maximal rep in the dataset was found to represent about 92% of a true rested 1RM on average. If you are entering an actual 1RM attempt, no calculation is needed — that weight is your 1RM.
Last updated: 2025-01-30 · Formula verified against primary sources.