One rep max calculator
Put a weight in with a single rep. Brzycki and Lombardi both return the weight itself, which is the only defensible answer: you lifted it once, so it is at most your one-rep max. Epley returns 103.3% of it, because its formula multiplies by (1 + reps ÷ 30) and never reaches 1 at one rep. Epley is the headline figure here by convention, and this is the one input where it is knowably wrong.
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.
Epley estimates one rep max as weight × (1 + reps ÷ 30), so five reps at 100 kg predicts about 117 kg. Brzycki gives 112.5 and Lombardi 117.5 for the same set. The three are different curves through similar data, and the gap between them is the most useful thing on the panel: it is the size of the uncertainty, made visible.
How to estimate your one rep max
The three formulas do not diverge in the direction most pages claim. Epley is linear in reps, Brzycki is a hyperbola, and they intersect at exactly ten reps, where both give 133.3% of the weight lifted. Below ten Epley reads higher: at five reps it is 116.7 against Brzycki's 112.5, a gap of nearly four per cent, and at a single rep it is 103.3 against 100. Above ten the order reverses and the gap widens fast. At fifteen reps Brzycki gives 163.6 against Epley's 150, and Brzycki's denominator of 37 minus reps means it heads for infinity as the set approaches 37. Lombardi, weight × reps to the power 0.1, is the one that catches people out, because it starts high and then flattens. Across the two to five reps this page recommends it is the highest of the three: at five reps it gives 117.5 against Epley's 116.7 and Brzycki's 112.5. It then crosses below Epley at around six reps and below Brzycki at around eight, and by fifteen it is much the lowest of the three at 131.1. Like Brzycki it returns the weight itself at one rep.
That behaviour at one rep is the clearest illustration of what these equations are. None of them is a law. They are curve fits to sets of roughly one to ten reps, and Epley's convenient linear form is what makes it overshoot at the boundary where the answer is already known.
For practical use the guidance follows from the arithmetic, not from any study: take the estimate from a set of five or fewer, where all three sit within about five per cent of each other, and pick one formula and stay with it. Switching between them mid-programme manufactures progress or regression that did not happen. Consistency is worth more here than being marginally closer to a true maximum nobody has measured.
The percentage rows are what most training blocks actually consume. A programme written at 80% needs a 1RM figure to multiply, and deriving it from a heavy triple is safer and less fatiguing than testing a genuine maximum every cycle.
What people use it for
- Setting working weights for a strength programme
- Tracking progress without maximal testing
- Comparing lifts across a training block
- Seeing how much the three formulas disagree at your rep count
Questions
Epley: weight × (1 + reps ÷ 30). Five reps at 100 kg gives about 117 kg. Brzycki uses 36 ÷ (37 − reps) and Lombardi uses reps to the power 0.1.
Any of them, consistently. Epley is the most widely used and is the headline here. Switching between them between training blocks creates progress that is arithmetic rather than strength.
At the extremes. They are identical at exactly ten reps. Below that Epley reads higher, by about four per cent at five reps. Above ten Brzycki reads higher, and by fifteen reps it is nine per cent above Epley.
Because its multiplier is 1 + reps ÷ 30, which is 1.033 at one rep rather than 1. Brzycki and Lombardi both return the weight itself, which is the correct answer for a single.
Five or fewer. All three formulas were fitted to short sets and they agree closely there. A set of fifteen measures muscular endurance, and endurance and maximal strength are only loosely related.
Rarely. It is fatiguing, it carries injury risk, and it needs a proper warm-up and preferably a spotter. A heavy triple gives most of the information at a fraction of the cost.