One Rep Max Calculator

What a one rep max estimate is really doing

A one rep max is the heaviest weight you can move for a single clean repetition. Testing it directly is stressful, fatiguing and — with a bar on your back — occasionally dangerous. So the standard approach is to take a set you already did, note the weight and the reps, and work backwards through a relationship between load and repetitions that has been measured across thousands of lifters.

Every formula here does the same thing: it assumes the number of reps you can perform at a given percentage of your max is reasonably consistent between people. That assumption holds well for low reps and gets shakier as the set gets longer, because a 15-rep set is testing muscular endurance as much as strength.

Worked example 1: a heavy triple

You squat 140 kg for 3 reps. Epley gives 140 x (1 + 3/30) = 154 kg. Brzycki gives 140 x 36 / (37 - 3) = 148.2 kg. The five formulas land between roughly 148 and 155 kg — a 7 kg spread on a 150 kg lift, under 5 percent. That spread is the honest precision of the method, and it is why the tool prints a range next to the single number.

Worked example 2: the same lift for ten reps

Now you bench 80 kg for 10. Epley: 80 x (1 + 10/30) = 106.7 kg. Brzycki: 80 x 36 / 27 = 106.7 kg. They agree here, but Lombardi returns about 100.7 kg and Wathan about 110 kg. The spread has widened to nearly 10 percent because ten reps depends heavily on conditioning and pacing. Use high-rep estimates to track progress over time, not to choose an opener at a meet.

Worked example 3: turning the estimate into training weights

With a 150 kg estimated max, a 5x5 at 80 percent is 120 kg, a heavy single at 95 percent is 142.5 kg, and a back-off set at 65 percent is 97.5 kg. The percentage table does this arithmetic for you. If the prescribed weight feels far heavier or lighter than the rep target suggests, your estimate has drifted — recalculate from a recent hard set rather than an old one.

Percent of max and what it usually buys you

Where these estimates go wrong

Lift selection matters. Deadlifts and squats tend to follow the formulas closely; bench press estimates run a little high for many lifters; olympic lifts do not fit the model at all, because a snatch is limited by technique and speed rather than by how long you can grind. Isolation movements are also unreliable — nobody performs a true one rep max on a lateral raise.

Training age matters too. Beginners often out-perform their estimates because their limiting factor is skill rather than force production, while very experienced lifters with high rep endurance can estimate higher than they actually lift on the day. Fatigue, sleep and how far the set was from failure all move the number: a set of 5 with three reps left in the tank is a different data point from a set of 5 that nearly stopped you.

The practical approach is to recalculate every few weeks from your best recent set, treat the result as a planning tool rather than a personal record, and let the bar have the final word. If 85 percent feels like a limit single, the estimate is too high — trust what the weight tells you.