One-Rep Max Calculator
Enter the weight you lifted and how many reps you got, and the calculator estimates your one-rep maximum using several established formulas.
Estimate your 1RM
Estimated 1RM
— kg
Estimates by formula
| Formula | Estimated 1RM |
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Loads as percentages
| %1RM | Load | Est. reps |
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Your numbers
Save an estimate and it fills in across the other calculators, and you can see it change over time. Everything stays in this browser — nothing is sent to a server or an account.
How this calculator works
One-rep max formulas rest on the observation that reps and relative load follow a fairly regular relationship: the lighter the load, the more reps you can complete with it. Each formula models that relationship slightly differently, which is why they produce different estimates from the same set.
The Epley formula (1985) is the most widely used: a straight line in which every rep adds the same amount to the estimate. The Brzycki formula (1993) is the most cautious at low rep counts but climbs steeply past ten reps. The Lombardi power function does the opposite: it gives the highest estimate at 1–5 reps and the lowest at high rep counts. The Wathan exponential formula tracks close to Epley, and O'Conner's shallower straight line gives consistently low estimates.
Since no single formula is objectively correct, the calculator shows the average of all of them by default. In practice that is a more reliable starting point than any one formula alone.
Frequently asked questions
How accurate is the estimate?
The estimate is typically within a few percent of a true tested max when the set was 1–5 reps and taken close to failure. As reps go up, the margin of error widens, because muscular endurance starts to influence the result more than maximal strength.
Do the formulas work for every exercise?
Not equally well. They were developed mainly for multi-joint barbell lifts such as the bench press, squat and deadlift. Single-joint movements and machines usually allow more reps at the same relative load, so the formula underestimates the max.
Does the set need to be taken to failure?
For accuracy, yes, or very close to it. If you left two or three reps in reserve, the calculator will underestimate your max by roughly the same margin.
Is the Epley formula accurate?
Epley is as accurate as the other established formulas, which is to say accurate enough for programming and not accurate enough to replace a tested max. It tends to sit at the higher end of the estimates, particularly above five reps. Rather than picking one formula, this calculator shows all five and averages them, so you can see how much they disagree — at three reps the spread is a few kilos, at fifteen it can exceed thirty.
Results are estimates and do not replace advice from a coach or healthcare professional.