Estimate your max from a set of any number of reps.
Source: LeSuer et al., J Strength Cond Res 1997 (formula by Epley, 1985).
What does one-rep max mean?
Your one-rep maximum (1RM) is the greatest load you can lift for a single complete repetition with proper form. It is the gold-standard measure of muscular strength for any exercise and forms the basis of percentage-based training programmes used by powerlifters, Olympic weightlifters, and strength coaches worldwide.
The Epley formula, proposed by Boyd Epley at the University of Nebraska in 1985, estimates your 1RM from a sub-maximal set: 1RM = weight × (1 + reps ÷ 30). It assumes that each additional repetition beyond the first reduces the sustainable load by approximately 1/30th. A comparison study by LeSuer and colleagues (1997) in the Journal of Strength and Conditioning Research tested seven prediction equations and found the Epley formula among the most accurate across different exercises.
The practical value of knowing your 1RM is that it allows you to prescribe training loads as percentages, for example, "perform 4 sets of 6 at 80% of 1RM." This enables progressive overload to be systematically planned and tracked. Testing a true 1RM carries some injury risk, so the estimated 1RM from a training set is often used as a safer proxy, especially for beginners.
Accuracy is best when using 2–10 repetitions for the input. Beyond 10 reps, individual differences in muscular endurance dominate and predictions become less reliable. A person who can bench press 80 kg for 12 reps has a different endurance profile from someone who can press 90 kg for 8 reps, even if both predict similar 1RMs.
Training percentages
| % of 1RM | Rep range | Training focus |
|---|---|---|
| 50 – 60% | 15 – 20+ | Muscular endurance, technique |
| 65 – 75% | 10 – 15 | Hypertrophy (size), metabolic conditioning |
| 75 – 85% | 5 – 10 | Strength-hypertrophy, general strength |
| 85 – 95% | 2 – 5 | Maximal strength development |
| 95 – 100% | 1 – 2 | Peaking, competition preparation |
When should you see a doctor?
Heavy strength training is safe for most healthy adults. However, before testing a true 1RM or starting any high-intensity resistance training programme, consult a doctor if you have cardiovascular disease, joint conditions, osteoporosis, or recent musculoskeletal injuries. Always use a competent spotter for barbell exercises and learn proper technique before adding heavy loads.
Frequently asked questions
How accurate is the Epley 1RM formula?
The Epley formula is most accurate when used with sets of 2–10 repetitions. Accuracy decreases significantly above 10 reps because individual endurance capacity becomes a larger factor. A comparison study by LeSuer et al. (1997) found the Epley formula to be among the most accurate of the common 1RM prediction equations. Expect an error range of roughly ±5–10% in practice.
What percentage of my 1RM should I train at?
Common training prescriptions: 65–75% of 1RM for 8–12 reps (hypertrophy), 75–85% for 5–8 reps (strength-hypertrophy), 85–95% for 1–5 reps (maximal strength), above 95% for true near-max training. For beginners, training at 60–70% of 1RM with higher reps (12–15) provides an effective and safe starting point.
What is the Epley formula for 1RM?
The Epley formula is: 1RM = weight × (1 + reps/30). For example, if you lift 80 kg for 8 reps: 1RM = 80 × (1 + 8/30) = 80 × 1.267 = 101.3 kg. The formula was proposed by Boyd Epley at the University of Nebraska in 1985 and subsequently validated in multiple comparison studies.