One rep max calculator

Because there is no single formula. Each one was fitted on a different group of lifters, on different exercises, and they disagree by design. With 80 kilograms for eight repetitions the spread between the highest and the lowest is over six kilograms.

A calculator that picks one and shows the number alone hides exactly the uncertainty you need. This one shows all five and writes the range, and the headline number is the median rather than the average, so a formula that strays does not drag the result.

Because it is already your maximum for that set. There is nothing to estimate.

It is worth saying because the formulas do not agree even here: with one repetition Epley returns 1.033 times the weight and O'Conner 1.025, inventing about three percent of load that nobody lifted. The tool returns the weight itself instead.

Close enough to plan training when the set is short. Below about ten repetitions the formulas sit within a few percent of each other and of a tested maximum.

Above ten the estimate loses its footing, because that is outside the range the formulas were fitted on and endurance starts deciding the set instead of strength. The tool says so on screen rather than handing you a number that looks exact.

It is an estimate from one set, not a measured maximum. It assumes the set was taken to the point where another repetition was not possible, so if you stopped with something left in the tank the real maximum is higher than what is shown, and if your form broke down it is lower.

Treat it as a starting point for choosing training loads, not as a target to attempt cold.