The Epley Formula, Explained
One equation from 1985 still runs most strength programs. Here is exactly what it says.
The Epley formula states 1RM = weight x (1 + reps/30): each completed rep suggests about 3.33 percent more than the lifted weight. Published by Boyd Epley in 1985, it remains the default 1RM estimator in coaching, slightly optimistic versus Brzycki.
The equation
1RM = w x (1 + r/30), where w is the weight lifted and r is the reps completed. The 30 in the denominator means each rep adds 1/30 (3.33 percent) of the weight to the predicted max. Ten reps predicts a max 33 percent above the set weight, which matches observed data well in the mid-rep range.
Worked examples
135 x 10: 135 x 1.333 = 180. 225 x 5: 225 x 1.1667 = 262.5. 315 x 3: 315 x 1.1 = 346.5. 185 x 12: 185 x 1.4 = 259, though at 12 reps treat this as optimistic. The mental shortcut: reps divided by 30 is the percentage bump, so 6 reps adds about 20 percent and 3 reps adds about 10 percent.
Origin
Boyd Epley, the pioneering strength coach at the University of Nebraska, published the formula in 1985 in his work on strength training. It came from observing how Nebraska football players' rep performances related to their tested maxes, and it has survived four decades of validation because the underlying relationship is genuinely close to linear in the useful rep range.
Epley vs Brzycki in practice
Epley runs 1 to 3 percent higher than Brzycki across most rep ranges. For programming volume and hypertrophy work the difference is noise. For setting heavy single attempts, many coaches use Brzycki or split the difference, because overshooting a max attempt has worse consequences than undershooting a training load.
Skip the arithmetic
Run the Epley formula on your latest hard set.
Epley formula questions
What is the Epley formula?
The Epley formula predicts one rep max as weight multiplied by (1 + reps/30). Each completed rep adds roughly 3.33 percent to the estimated max.
Who created the Epley formula?
Boyd Epley, the pioneering strength coach at the University of Nebraska, published the formula in 1985 based on his football players' training data.
Is Epley accurate?
Yes, within a few percent for hard sets of 1 to 10 reps. It runs slightly optimistic compared to Brzycki, so conservative programmers prefer Brzycki for heavy singles.
What is the 3.33 rule?
Since Epley adds reps/30 per rep, each rep contributes about 3.33 percent: 3 reps is ~10 percent, 6 reps ~20 percent, 9 reps ~30 percent above the set weight.