One Rep Max Calculator
Estimate your one-repetition maximum (1RM) from any set using four validated formulas — Epley, Brzycki, Lander, and O'Conner — and instantly see predicted maxes across rep ranges. Use it to set training loads without risking a true max attempt.
About this calculator
A one-rep max (1RM) is the maximum weight you can lift for exactly one full repetition. Rather than testing this directly — which carries injury risk — you can estimate it from a submaximal set. The four formulas supported are: Epley: 1RM = weight × (1 + reps/30); Brzycki: 1RM = weight × 36/(37 − reps); Lander: 1RM = weight × 100/(101.3 − 2.67123 × reps); O'Conner: 1RM = weight × reps^0.10. Once the 1RM is estimated, target rep-range percentages are applied: 1 rep = 100%, 3 reps ≈ 93%, 5 reps ≈ 87%, 8 reps ≈ 80%, 10+ reps ≈ 75%. These percentages allow coaches and athletes to prescribe training loads at specific intensities across any program. Accuracy is best when the input set falls between 2 and 10 reps.
How to use
Example: You bench press 100 kg for 5 reps using the Epley formula, and want to know your 3-rep max. Step 1 — Estimate 1RM: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg. Step 2 — Apply the 3-rep percentage: 116.7 × 0.93 = 108.5 kg. Your estimated 3RM is approximately 108.5 kg. To find your 5RM training load: 116.7 × 0.87 = 101.5 kg. Use these figures to set working weights in percentage-based programs like 5/3/1 or linear periodization.
Frequently asked questions
Which one rep max formula is the most accurate for strength training?
Research suggests the Brzycki and Epley formulas perform similarly well for sets in the 2–10 rep range, which covers most practical training scenarios. The Epley formula tends to slightly overestimate at higher rep counts (above 10), while Brzycki becomes mathematically unstable near 37 reps. The Lander formula was derived specifically from powerlifting data and can offer marginally better accuracy for compound movements like squat and deadlift. For best results, test with a set of 3–6 reps where fatigue is minimal and technique is not compromised.
How do I use my 1RM to set training weights for a powerlifting or strength program?
Most percentage-based strength programs prescribe work sets as a fraction of your 1RM — for example, 5 sets of 3 at 85% 1RM. Once you have an estimated 1RM from this calculator, multiply it by the prescribed percentage to get your working weight. For example, a 150 kg squat 1RM at 85% gives a working set weight of 127.5 kg. Re-test or re-estimate your 1RM every 4–8 weeks as you get stronger to keep the percentages accurate and progressive.
Why are one rep max estimates less accurate for sets above 10 reps?
At higher rep ranges, factors beyond pure strength — such as cardiovascular fitness, muscular endurance, and pain tolerance — increasingly determine how many reps you can complete. This means the relationship between a high-rep set and a true 1RM becomes less predictable and more individual. All common 1RM formulas assume a relatively linear strength-endurance curve that holds well up to about 10 reps but diverges significantly beyond that. For the most reliable estimate, perform your test set with a load you can lift for 3–6 clean repetitions.