What is the Epley formula?

The Epley formula estimates one-rep max as: 1RM = Weight × (1 + Reps ÷ 30). Developed by Boyd Epley at the University of Nebraska in 1985, it's the most widely cited 1RM prediction equation in strength training research.

How accurate is the Epley formula?

The Epley formula has a correlation of r = 0.85–0.95 with actual 1RM testing. It's most accurate in the 3–10 rep range on compound lifts, with precision of ±5–8% for trained individuals.

Is Epley or Brzycki more accurate?

For 1–10 reps, both produce nearly identical results. Above 12 reps, Brzycki estimates climb steeply toward its asymptote at 37 reps, while Epley rises linearly. Both become less reliable at high rep counts, and neither should be treated as definitive above 12 reps.

Why do 1RM estimates become less reliable at high reps?

All prediction formulas assume a fixed mathematical relationship between reps and %1RM. In practice, fatigue accumulates non-linearly at higher rep counts, and individual variation (muscle fiber type, endurance capacity) has a larger effect. Stick to 3–10 rep inputs for best accuracy.

Epley Formula Calculator

Name: Epley Formula Calculator
Author: Manish Kumar

Formula	1RM (kg)
Epley	116.7
Brzycki	112.5
Lombardi	117.5
Mayhew	119
Wathen	116.6
O'Conner	112.5

Reps	Epley	Brzycki	Diff
1	100	100	0
3	110	105.9	+4.1
5	116.7	112.5	+4.2
8	126.7	124.1	+2.6
10	133.3	133.3	0
12	140	144	-4
15	150	163.6	-13.6
20	166.7	211.8	-45.1

Reps	Weight	%1RM
1	116.7	100%
2	109.5	93.8%
3	106.1	90.9%
4	102.9	88.2%
5	100	85.7%
6	97.2	83.3%
7	94.6	81.1%
8	92.1	78.9%
9	89.7	76.9%
10	87.5	75%
11	85.4	73.2%
12	83.3	71.4%
13	81.5	69.8%
14	79.6	68.2%
15	77.8	66.7%
16	76.1	65.2%
17	74.5	63.8%
18	72.9	62.5%
19	71.4	61.2%
20	70	60%

%1RM	Weight (kg)
100%	116.7
95%	110.9
90%	105
85%	99.2
80%	93.4
75%	87.5
70%	81.7
65%	75.9
60%	70
55%	64.2
50%	58.4

Key Takeaways

The Epley formula (1RM = Weight × (1 + Reps ÷ 30)) is the most widely cited one-rep-max prediction equation in strength research.^[1]
It correlates at r = 0.85–0.95 with actual 1RM testing across compound lifts, with best accuracy in the 3–10 rep range.^[2]
Above 12 reps, both formulas become less reliable — Brzycki accelerates toward its asymptote at 37 reps, while Epley rises linearly. Stick to 3–10 rep inputs for trustworthy results.^[3]

How the Epley Formula Works

1RM = Weight × (1 + Reps ÷ 30)

Developed by Boyd Epley, University of Nebraska, 1985

The Epley equation assumes a linear relationship between reps and percentage of 1RM. Each additional rep reduces the load by approximately 1/30 (~3.3%) of the maximum.^[1]

For an alternative approach that caps at 36 reps, see the Brzycki Equation Calculator. For multi-formula comparison, use the One Rep Max Calculator.

Epley vs Brzycki: Key Differences

Low reps (1–6): Both formulas produce nearly identical results — differences are typically less than 1%.
Mid reps (7–10): Epley tends to estimate slightly higher than Brzycki, with divergence growing as reps increase.
High reps (12+): Brzycki estimates climb steeply as reps approach its asymptote at 37, while Epley continues rising linearly. Both become unreliable, but they diverge in opposite directions — Brzycki accelerates upward while Epley stays linear.
Both have limits: Epley has no mathematical ceiling, and Brzycki approaches infinity at 37 reps. Neither formula should be relied upon above 12 reps without cross-referencing actual test data.

For most practical purposes (3–10 reps on compound lifts), both formulas are equally reliable.^[2]

Limitations and Important Notes

All 1RM prediction formulas are estimates based on population data — individual variation depends on fiber type, training history, and fatigue tolerance.
Accuracy is highest for compound movements (bench press, squat, deadlift) in the 3–10 rep range.
All 1RM formulas (including Epley and Brzycki) become increasingly unreliable above 12 reps. Use 3–10 rep data for the most accurate estimates, and consider the Mayhew or Wathen formulas for mid-range rep counts.
This tool is for informational and journaling purposes only. It does not constitute personalized advice.

Frequently Asked Questions

Sources & References

Accuracy of seven equations for predicting 1-RM performance of apparently healthy sedentary older adults. Knutzen KM, Brilla LR, Caine D. Measurement in Physical Education and Exercise Science (1999)
Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Various. PMC (2024)
Estimation of a one repetition maximum bench press for untrained women. Various. J Strength Cond Res (1998)

Manish Kumar

Certified Personal Trainer & Sports Nutritionist

NASM-CPTCertified Sports Nutritionist10+ Years Experience500+ Clients Coached

NASM-certified fitness and nutrition coach with over 10 years of hands-on experience helping people build strength, lose fat, and live healthier lives. Specializing in gym-based workouts with a strong focus on lifting technique, biomechanics, and practical exercise science. Through FitLifeRegime, sharing the tools, tips, and insights that have worked for hundreds of clients — helping you start your own fitness journey with confidence and clarity.

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Certified Personal Trainer & Sports Nutritionist from the National Academy of Sports Medicine

This tool is for informational and journaling purposes only.

I am NOT a doctor.

Epley Formula Calculator