Your one-rep max (1RM) is the most weight you can lift for a single rep with good form. It's the standard measure of absolute strength for a given exercise.

You rarely need to actually attempt a true 1RM — grinding out a max single is taxing and carries injury risk. Instead, this calculator estimates it from a set you already did.

For best accuracy, use a set where you reached close to failure — ideally between 3 and 10 reps. Very high-rep sets (15+) become less reliable because fatigue and technique break down before true muscular failure.

This calculator uses the Marzagão weight-dependent formula, which adjusts the rep-to-1RM relationship based on how heavy the working weight is. Heavier loads yield a different fatigue curve than lighter loads, so a single fixed multiplier (like Epley or Brzycki) systematically over- or under-estimates at the extremes.

The formula is undefined for very low weights (where the denominator −2.55 + 4.58 × ln(w) approaches zero), so the calculator shows — in those cases.

When rounding is enabled, the estimated 1RM is floored to the nearest loadable increment (5 lb / 0.5 kg), so the result is always a weight you can actually put on the bar.

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Enter your bodyweight to see how your 1RM compares to strength standards.