Your one-rep max is the most you can lift once with good form, and it anchors strength programming. Instead of testing it directly each time, you can estimate it from a heavier set taken near failure. Two formulas dominate: Epley (1RM = weight × (1 + reps/30)) and Brzycki (1RM = weight × 36/(37 − reps)). They agree closely for low reps and diverge as reps climb, so they're most trustworthy for sets of about ten or fewer. From the 1RM you set working weights as percentages.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the Epley and Brzycki 1RM formulas. Not medical advice.
The 1RM formulas
Both formulas inflate the lifted weight by an amount that grows with reps — a set of 5 implies a higher single than a set of 2 at the same weight. Epley scales linearly with reps, while Brzycki uses a ratio that rises faster as reps approach the high teens (where it breaks down, since the denominator shrinks). Averaging the two is a sensible working estimate. Percentages then convert the 1RM into daily training loads for strength or hypertrophy.
Worked example — 100 kg for 5 reps
Scenario: you lift 100 kg for 5 solid reps.
Epley estimates about 116.7 kg and Brzycki 112.5 kg, so a sensible working 1RM is the average, roughly 114.6 kg. From there, 85% (a common strength-day load) is about 97 kg, 80% about 92 kg, and 90% about 103 kg. The two formulas sit within a couple of kilos here because 5 reps is well inside their reliable range; push the rep count toward 15+ and the spread widens, which is why heavy sets of 3–6 reps give the cleanest estimate.
Frequently Asked Questions
The heaviest weight you can lift once with good form — the reference for strength and loads.
Epley w×(1+reps/30) or Brzycki w×36/(37−reps). 100×5 → 116.7 / 112.5.
≤ 10 reps near failure; 3–6 reps gives the closest estimate. High reps overestimate.
% of 1RM: ~100% 1 rep, 90% 4, 80% 8, 70% 12. Higher % for strength, moderate for size.
Only with a warm-up, good form and a spotter. Beginners should estimate and train submaximally.