1RM Calculator: Epley vs Brzycki Comparison
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/8/2026
The Epley and Brzycki formulas both estimate 1RM from a weight and a number of reps, but give slightly different results. For 100 kg lifted 5 times, Epley estimates about 116.7 kg, Brzycki about 112.5 kg — a gap of more than 4 kg between the two.
Explanation
Several well-known formulas exist for estimating the 1RM (the theoretical maximum load liftable for a single rep) from a performance done with more than one rep, each developed independently and calibrated on different data. Our 1RM calculator uses the Epley formula (1RM = weight × (1 + reps ÷ 30)), the most widely cited. The Brzycki formula, developed by Matt Brzycki, proposes a slightly different relationship: 1RM = weight ÷ (1.0278 − 0.0278 × reps). At a single rep, Brzycki gives back exactly the weight lifted (its denominator equals 1 by construction), while Epley always stays slightly above (an excess of weight ÷ 30, or about 3.3% at one rep) — the two formulas therefore never converge perfectly, even at the closest point to the actual 1RM. This gap, already present at one rep, then widens as the number of reps increases: Epley tends to give a more generous estimate than Brzycki beyond a few reps, a gap that can reach several kilograms by 5 reps. Neither formula is 'the correct one' in absolute terms: both are approximate statistical models, calibrated on different populations and exercises, and the gap between them gives a concrete indication of the real uncertainty of any formula-based 1RM estimate, rather than a direct measurement. Both remain more reliable between 1 and 10 reps; beyond that, muscular endurance comes into play more and the estimate becomes less representative of actual maximum strength. The only truly reliable measure of 1RM remains a direct test on a single rep, under safe conditions and with a proper warm-up (see our strength training warm-up calculator).
Example: 100 kg lifted 5 times
Inputs
Weight lifted: 100 kg. Reps: 5.
Calculation
Epley = 100 × (1 + 5 ÷ 30) = 100 × 1.1667 ≈ 116.7 kg. Brzycki = 100 ÷ (1.0278 − 0.0278 × 5) = 100 ÷ 0.8888 ≈ 112.5 kg. Gap ≈ 4.2 kg.
Result
The two formulas give 1RM estimates differing by more than 4 kg for this same performance.
Frequently asked questions
Which formula is more reliable, Epley or Brzycki?
Neither is universally recognized as superior: they were calibrated on different populations and protocols, and their relative accuracy varies by exercise, number of reps, and the profile of the person tested. The gap between the two estimates, shown by this calculator, actually gives a useful indication of the real uncertainty to account for, rather than searching for a single definitive result.
Why does the gap between the two formulas grow with the number of reps?
Because the two formulas follow slightly different mathematical curves (a linear relationship for Epley, a fractional relationship for Brzycki), which coincide almost exactly near a single rep but progressively diverge as the number of reps moves away from this common reference point. This is why both formulas are considered more reliable over a limited rep range (generally 1 to 10), where this divergence stays moderate.
Should these formulas be trusted to choose a precise training load?
These formulas give a useful order of magnitude for planning a training program (see our load from 1RM percentage calculator), but remain statistical estimates, not an exact measurement. For a competition load or a precise performance goal, a direct 1RM test, done progressively and safely, remains the only truly reliable measure.