One-Rep Max Calculator (5 formulas + percent table)

What 1RM is and why it matters

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It's the gold standard for measuring strength and the basis for percentage-based programming (5×5 at 80%, 3×3 at 90%, etc.). Many lifters never test their 1RM directly because the attempt is fatiguing and risky — instead they estimate it from submaximal lifts.

Estimating from a 5-rep set or 8-rep set has been validated against actual 1RM tests in multiple studies. Within ±5% accuracy is typical for sets of 1-10 reps. Above 10 reps, accuracy drops because endurance becomes a factor and form often breaks down.

Why we use five formulas

Each formula was validated on different populations and exercises, so each has slight biases. Averaging gives a more robust estimate.

Epley (1985): w × (1 + reps/30). Most popular; tends to overestimate slightly at high reps. Often the default in fitness apps.

Brzycki (1993): w × 36 / (37 − reps). Conservative; tends to be lower than Epley. Used in NSCA literature.

Lombardi: w × reps^0.10. The most aggressive at high reps; less commonly used.

O'Conner: w × (1 + 0.025 × reps). Linear; simplest to compute mentally.

Lander: 100w / (101.3 − 2.67123 × reps). Used in the bench-press research that produced the formula.

Using the percentage table for programming

Once you know your 1RM, the percentage table tells you what weight to use for various rep ranges. 5×5 work is typically done at 80-85% of 1RM (about 5RM weight); 3×3 strength sets at 90% (3RM); pyramids might hit 70% for 10s, 80% for 5s, 90% for 3s.

These percentages are starting points. If your last set leaves you with 2-3 reps in reserve, the weight is right. If you grind out reps and the weight crushes you, drop 5-10%. If you bang out double the prescribed reps easily, your 1RM is higher than estimated and you should retest.