Enter the weight you lifted and the number of repetitions performed to estimate your one‑rep max (1RM) using popular strength‑training formulas.
A set of 5 reps at 100, run through all four options.
Between 112.50 and 119.01 depending on the formula — a spread of about 6 percent on the same set.
A five-rep set at 100 produces estimates from 112.5 to 119 here. None of them is the true answer, because none of them knows anything about you. Pick one formula and stay with it: the value of a 1RM estimate is in tracking the same calculation over time, and switching formulas between sessions creates progress or regression that exists only in the arithmetic.
These equations were fitted around low-rep sets and get less reliable the further you go from a single. At two or three reps the estimates cluster tightly and mean something; at ten or twelve they diverge and are strongly affected by how much muscular endurance you happen to have relative to maximal strength. The field stops at 12 for that reason. If you want a number you can act on, test with a heavy set of three to five rather than a light set of twelve.
Every one of these formulas assumes the set was taken close to failure. Five reps with three left in the tank is not the same input as five hard reps, and it will understate the estimate significantly. If you routinely stop well short, your calculated maximum will drift below your real one, which is safer than the reverse but makes the number useless for programming.
Its main use is setting working loads as a percentage. Once you have a figure, training percentages are simple multiplication — 80 percent of a 116.67 estimate is 93.3. Treat the estimate as provisional, recalculate it whenever you hit a genuinely hard set at a new load, and never load a bar for an actual maximal attempt based on arithmetic alone without appropriate safety measures in place.
There is no single winner — accuracy varies with the lift, the athlete and the rep range, and each formula was fitted on a different population. Epley and Brzycki agree closely at low reps and separate as reps climb. What matters more than the choice is consistency: use the same formula every time so that changes in the output reflect changes in your strength rather than changes in the equation.
Because the estimates stop meaning much beyond that. All four formulas are extrapolations, and the further the set is from a single repetition the more the result depends on endurance rather than maximal strength. Beyond about twelve reps the different formulas can disagree by 20 percent or more on the same set.
Whichever you entered. The calculation is a pure multiplication and involves no unit conversion, so the output unit always matches the input unit.
That is its most reliable use. Multiply the estimate by the percentage a programme calls for and round to the nearest available plate. It is a much safer way to select loads than attempting true maximums frequently, and it works even when the absolute estimate is a little off, because the percentages scale with it.
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