Estimate a one-rep max with Epley’s formula

Epley treats a set of n reps at load w as w × (1 + n/30). At 1 rep you get w back. At 10 reps you multiply by 1.33. Past about 10–12, fatigue and technique make the extrapolation poor. Other formulas (Brzycki, Lombardi) exist; this one is simple and common.

1RM = w × (1 + n/30)

An empirical estimate, not an NSCA testing protocol. No rest interval, no squat depth, no dumbbell vs barbell split. Units cancel: kg or lb, the 1RM is in the same unit.

Load lifted

Load of the set, one unit.

Reps

Complete reps. 1 to 12; beyond that the model is rejected.

Assumptions

• Complete reps, same range of motion.
• No outside assistance.
• Epley’s formula only.

Limits

• Not a real 1RM test.
• Poor past about 10 reps.
• Not coaching.

Useful for programming percentages (5×5 at 80% of an estimated 1RM). Dangerous if you load the bar to the number without a spotter. A true 1RM is tested, with stable technique.

• Entering 20 reps.

  The field stops at 12: past that, change formula or test another way.

• Mixing kg and lb.

  Use one unit; the 1RM comes back in that unit.

• Loading the estimated 1RM with no safety.

  It is an estimate, not a max-attempt instruction.

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Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

This calculation uses a standard mathematical identity. See also the methodology.