One rep max calculator
Every 1RM formula is fitted to sets of about one to five reps and starts drifting beyond that. A set of fifteen says far more about your muscular endurance than your maximum strength, and the estimate from it can be ten per cent out in either direction. If the number matters, test from a set of five or fewer.
An estimate. Attempting a true one-rep max requires a proper warm-up, correct technique and ideally a spotter. Do not test a maximum on a lift you have not trained.
The Epley formula estimates one rep max as weight × (1 + reps ÷ 30). Five reps at 100 kg predicts a 1RM of about 117 kg. Estimates are most reliable from sets of five or fewer and drift noticeably beyond that.
How to estimate your one rep max
Epley, Brzycki and Lombardi come from different fits to different data and diverge as reps rise. At three reps they agree within a per cent or two; at ten they can differ by five per cent or more. Which one to prefer is largely arbitrary — the useful move is to pick one and stay with it, since consistency matters more than which curve is marginally better. The percentage rows are what most programmes actually consume: a training block prescribed at 80% needs a 1RM figure, and a formula-derived one is safer than testing a true maximum every cycle.
Questions
Epley: weight × (1 + reps ÷ 30). Five reps at 100 kg gives about 117 kg.