Health Guide
Epley vs Brzycki — Why Two Formulas?
The two standard 1RM formulas agree at low reps and diverge as reps climb. What the gap between them tells you.
Last updated: August 29, 2026
Our One-Rep Max Calculator shows two numbers: an Epley estimate and a Brzycki cross-check. Showing two is deliberate, and the distance between them is useful information.
The two formulas
Epley (1985): 1RM = weight × (1 + reps / 30)
Brzycki (1993): 1RM = weight / (1.0278 − 0.0278 × reps)Both predict a one-rep max from a reps-to-fatigue set. They were derived independently and take different mathematical shapes — Epley is linear in reps, Brzycki is a reciprocal.
Where they agree and diverge
Using a 100 kg lift at various rep counts:
| Reps | Epley | Brzycki | Gap |
|---|---|---|---|
| 1 | 100.0 | 100.0 | 0.0 |
| 3 | 110.0 | 105.9 | +4.1 |
| 5 | 116.7 | 112.5 | +4.2 |
| 8 | 126.7 | 124.2 | +2.5 |
| 10 | 133.3 | 133.4 | −0.1 |
| 12 | 140.0 | 144.1 | −4.1 |
| 15 | 150.0 | 163.7 | −13.7 |
Two things stand out. They cross over around 10 reps — Epley reads higher below that, Brzycki higher above. And the gap widens sharply at high reps: at 15 reps they differ by nearly 14 kg on the same set.
The gap is a confidence signal
This is why we show both. When the two formulas are close, they agree, and your estimate is on relatively firm ground. When they diverge, neither deserves much trust.
A useful reading:
- Gap under ~5 kg — the formulas broadly concur. Reasonable estimate.
- Gap large and growing — you are in high-rep territory where 1RM prediction gets unreliable regardless of formula.
Rather than hiding this behind a single averaged number, showing both lets the disagreement do its job. It is the same reasoning as the protein target range — where the underlying certainty is limited, the display should show it.
Which one to use
We report Epley as the primary estimate because it is the more widely used of the two and behaves sensibly across the practical rep range. Brzycki serves as the cross-check.
If you want a single number for programming, take Epley. If the two are far apart, the more useful response is to re-estimate from a lower-rep set rather than to pick a favourite formula.
Neither knows your exercise
Both formulas apply the same relationship to every lift, and reps-to-max relationships genuinely differ by exercise. A set of five on a squat and a set of five on a bench press do not necessarily imply the same percentage of max.
They also cannot see technique, training history, or how well you tolerate maximal loads. This is part of why the calculator carries a moderate confidence rating — see how accurate are 1RM estimates.
The bottom line
Epley and Brzycki agree closely at low reps, cross over around 10, and diverge sharply beyond that. Use Epley as your working number, and read a wide gap as a signal to estimate from a lower-rep set instead. Both are on the One-Rep Max Calculator.
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