One Rep Max Formula Comparison Calculator

How the One Rep Max Formula Comparison Calculator Works

Rep-max equations turn a submaximal set into an estimated single, but their coefficients and curve shapes differ. This page holds the input constant, calculates five established methods, and exposes the amount of disagreement instead of hiding it behind a formula dropdown.

Estimate mode applies every formula to one weight and rep count. Reverse mode starts with a known 1RM and algebraically predicts the load associated with a target rep count. A one-rep input is normalized to the known load for all methods so the comparison has an intuitive anchor.

One Rep Max Comparison Formulas

Epley and Brzycki below use common rationalized variants (R/30 and 36/(37−R)). LeSuer and colleagues’ original 1997 table prints rounded coefficients 0.0333 and 100/(102.78−2.78R), so tiny numerical differences from that table are expected. The one-rep normalization is an explicit calculator convention.

Formula: Epley = W(1 + R/30); Brzycki = 36W/(37 − R); Lombardi = WR^0.10; Wathan = 100W/(48.8 + 53.8e^(−0.075R)); O’Conner = W(1 + 0.025R)

The median is the middle of the five sorted outputs and is less affected by one high or low estimate than the mean. Relative spread divides the maximum-minus-minimum range by the mean, making disagreement comparable across light and heavy lifts.

Choosing the Right Inputs

These equations assume a repetition-maximum set: the recorded rep count represents the repetitions possible at that load with consistent technique. An easier working set can underestimate. The calculator uses a conservative comparison scope of 1 through 10 repetitions. Accuracy varies with exercise and athlete; this limit does not validate every equation for every lifter.

Understanding Your Results

The median leads, followed by every method, each method’s difference from the median, the mean, full range, and relative spread. A narrow spread means these five equations happen to agree for the input; it does not prove the shared estimate is exact.

Track the same lift with the same formula or median convention over time. Switching formulas can create an apparent gain or loss without any performance change, especially at higher rep counts.

Worked Example

For 225 lb completed for eight reps, the five estimates range from 270.00 to 287.26 lb. The median is 279.31 lb, the mean is 279.72 lb, and the range equals about 6.17% of the mean.

Common Mistakes

Do not compare a bench-press estimate with a squat estimate, use repetitions that were stopped far from the intended effort, or treat the highest formula as automatically best. Nearest-increment rounding is a display comparison applied after raw calculations. It can round upward or to zero for a very small load, and does not identify a safe training load. Median, mean, spread and differences use unrounded values.

Assumptions and Limitations

Prediction error depends on the lift, athlete, technique, fatigue, and proximity to failure. The formulas were developed from particular samples and are not interchangeable with a directly tested one-rep maximum.

Sources

Matthew Brzycki. Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue, 1993.
Dale LeSuer and colleagues. The Accuracy of Prediction Equations for Estimating 1-RM Performance in the Bench Press, Squat, and Deadlift, 1997.
Daniel Wathan. Load Assignment in Essentials of Strength Training and Conditioning, 1994.
Boyd Epley. Workout, 1985.
Patrick Lombardi. Beginning Weight Training, 1989.
Robert O’Conner, Patrick Simmons, and Patrick O’Shea. Weight Training Today, 1989.

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