Multi-Formula One-Rep Max Calculator
Estimate your one-rep max as the average of five published 1RM formulas — Epley, Brzycki, Lombardi, Lander and O’Conner — instead of trusting a single equation.
How it works
Epley: w·(1+r/30) · Brzycki: w·36/(37−r) · Lombardi: w·r^0.10 · Lander: w·100/(101.3−2.67123r) · O’Conner: w·(1+r/40) · 1RM = average
Every 1RM formula is a regression fit to a different data set, so each one is a little high or low depending on rep range and the person. Averaging five well-known equations smooths out the quirks of any single formula and gives a more robust estimate than picking one. All of them lose accuracy above about 10–12 reps, where fatigue and technique diverge from raw strength, which is why this calculator caps reps at 12.
Worked example
For 100 kg × 5 reps: Epley 116.7, Brzycki 112.5, Lombardi 117.5, Lander 113.7 and O’Conner 112.5. The average is (116.7 + 112.5 + 117.5 + 113.7 + 112.5) ÷ 5 ≈ 114.6 kg estimated 1RM.
Frequently asked questions
Why average several formulas instead of using one?
Each formula was derived from a different sample and tends to over- or under-estimate in certain rep ranges. Averaging Epley, Brzycki, Lombardi, Lander and O’Conner cancels much of that individual bias, giving a steadier number to plan training percentages from.
How many reps give the most accurate estimate?
Accuracy is best at low reps — ideally 2 to 5. Beyond about 10 reps the relationship between reps and true 1RM breaks down, so treat high-rep estimates as rough.
Is an estimated 1RM safe to program from?
Yes, and it is safer than repeatedly testing a true max. Use the estimate to set working percentages, then adjust based on how the weights actually feel.
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Educational training estimate, not medical or coaching advice. Individual response varies — progress under qualified supervision.