One Rep Max Calculator
Estimate your one-rep max from any set of 1–20 reps with seven formulas (Epley, Brzycki, Lombardi, Mayhew, O’Conner, Wathan, Lander) and their average, plus a 50–100% training table and a rep-max chart in lb or kg.
How it works
Epley: w × (1 + r ÷ 30) · Brzycki: w × 36 ÷ (37 − r) · Lombardi: w × r^0.10 · Mayhew: 100w ÷ (52.2 + 41.9e^(−0.055r)) · O’Conner: w × (1 + 0.025r) · Wathan: 100w ÷ (48.8 + 53.8e^(−0.075r)) · Lander: 100w ÷ (101.3 − 2.67123r)
Each formula takes the weight of a hard set (w) and the reps you completed (r) and extrapolates to the heaviest single rep you could do. They were fitted on different groups of lifters, so they agree closely at low reps and drift apart past about 10: Brzycki and O’Conner run low, Mayhew and Lombardi run high. The calculator shows all seven, their range and their average, and you choose which one drives the training tables. If the set was not taken to failure, enter the reps you had left in the tank and they are added to the count. The percentage table gives the weight at 50–100% of your max with the reps you can typically do there, and the rep-max table turns the estimate back into the weight to expect for 1–20 reps. Training weights can be rounded to the plates you have.
Worked example
200 lb for 5 reps to failure. Epley: 200 × (1 + 5 ÷ 30) = 233.3 lb. Brzycki: 200 × 36 ÷ 32 = 225.0 lb. Lombardi 234.9, Mayhew 238.0, O’Conner 225.0, Wathan 233.2 and Lander 227.4 lb. The average of all seven is 231.0 lb, with a range of 225–238 lb. A training set at 80% is about 185 lb (rounded to 5 lb), where most lifters manage about 8 reps.
Frequently asked questions
Which one-rep max formula is most accurate?
None wins for everyone. Studies find Epley, Brzycki and Mayhew all within about 5% for 2–10 reps on the big barbell lifts, with Brzycki and O’Conner lower and Mayhew and Lombardi higher at high reps. The average of all seven smooths out each formula’s bias, which is why it is the default.
How many reps should my test set be?
A heavy set of 3–6 reps to failure gives the best estimate. Above about 10 reps endurance starts to matter and the formulas disagree more, so the calculator warns you.
What if I stopped before failure?
Enter the number of reps you think you had left in “Reps left in the tank”. They are added to your reps before the formulas run, so an easy set of 5 with 2 left counts as 7 reps to failure.
How do I use the percentage table?
Strength work usually sits at 80–95% for 1–6 reps, muscle-building at 65–80% for 6–12, and endurance or technique work at 50–65% for 15 or more. If a prescribed weight feels wrong on the day, adjust it; the table is a guide.
Should beginners test a true 1RM?
Usually not. Maximal singles are a skill of their own and carry the most injury risk before technique is stable. An estimated max gives beginners everything programming needs.
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Estimates are for training guidance. Lift with good technique, warm up properly and use a spotter or safety bars for heavy sets; check with a professional if you have an injury or health condition.