One Rep Max Calculator
Estimate the maximum weight you can lift for a single rep from a sub-maximal set. Use it to set training zones, track strength progress, or compare lifts across exercises.
About this calculator
Your one-rep maximum (1RM) is the heaviest load you can lift exactly once with good form. Rather than attempting a dangerous true max, you perform a set with a lighter weight for multiple reps and apply a predictive formula. The three most common are: Epley — 1RM = weight × (1 + reps / 30); Brzycki — 1RM = weight / (1.0278 − 0.0278 × reps); and Lombardi — 1RM = weight × reps^0.10. Epley tends to be accurate for lower rep ranges (1–10), Brzycki is widely used in powerlifting research, and Lombardi works across broader rep ranges. All formulas assume fatigue-free, full-effort repetitions — results become less reliable above 10 reps. Use your estimated 1RM to calculate training percentages (e.g., 75% of 1RM for hypertrophy work).
How to use
Suppose you bench-pressed 100 kg for 5 reps using the Epley formula. Step 1 — Enter weight = 100 kg and reps = 5. Step 2 — Select Epley. Step 3 — The calculator computes: 1RM = 100 × (1 + 5 / 30) = 100 × 1.1667 ≈ 116.7 kg. So your estimated 1RM is roughly 117 kg. You can now set your training loads: 80% of 117 kg ≈ 93.5 kg for strength sets, or 65% ≈ 76 kg for hypertrophy volume work.
Frequently asked questions
Which one rep max formula is most accurate for powerlifting?
The Brzycki formula is widely cited in powerlifting and sports science research as the most accurate for low rep ranges of 2–6 reps. It uses the equation 1RM = weight / (1.0278 − 0.0278 × reps), which accounts for the steeper strength drop-off at low rep counts. Epley is also highly regarded and tends to agree closely with Brzycki in the 3–6 rep range. For best results, test with 3–5 reps rather than 8 or more, as prediction error increases significantly at higher rep counts.
How do I use my 1RM to set training weights for different goals?
Once you have your 1RM estimate, multiply it by a target percentage based on your training goal. For maximal strength, use 85–95% of 1RM for sets of 1–3 reps. For hypertrophy (muscle building), work in the 65–80% range for 6–12 reps. For muscular endurance, use 50–65% for 15+ reps. These percentages come from well-established periodization models and allow you to autoregulate load across a training cycle without retesting your max every week.
Why does 1RM estimation become less accurate at higher rep counts?
All 1RM formulas assume a linear or near-linear relationship between reps performed and the percentage of maximal strength being used. Beyond about 10 reps, individual factors such as muscular endurance, cardiovascular fitness, and pain tolerance play a larger role than raw strength, causing the formulas to overestimate true 1RM. A set of 15 reps at a given weight may reflect endurance capacity as much as strength. For the most reliable estimate, keep your test set between 3 and 6 reps at a weight that genuinely challenges you by the final repetition.