Max Reps at Percentage
Enter your one rep max and a working percentage to estimate reps in the tank, RPE, and volume.
Fill in the form and your result lands here.
Learn the details
This tool reads a fixed percentage-to-reps chart and interpolates between its rows, rather than evaluating a formula. The chart is a blend: its heavy end sits close to Brzycki, its light end follows Epley, and the two disagree sharply down there. At 50% this returns 30 reps where Brzycki would predict about 19. Treat everything far from your true max as a rough guide.
Rep-max charts look like physics and behave like weather forecasts. Here is what this one is doing under the hood, where it is trustworthy, and why the number you actually hit in the gym will not match it exactly.
What the tool is doing
This is not a live formula. It is a fixed percentage-to-reps chart, eleven rows from 100 percent down to 50 percent, with straight-line interpolation between rows for anything you type in between. Those rows are the standard values you see in most gyms, drawn from the two classic rep-max equations, Epley and Brzycki. Both take a weight and a rep count and fit a line through population averages. They disagree more than people realise: at 50 percent of your max, Epley predicts about 30 reps and Brzycki predicts about 19. This chart carries the Epley-style number down there and the Brzycki-style numbers up top, so call it a blended standard rather than one named formula.
A worked example
Enter a 315 pound max and ask for 75 percent. The tool takes 236.25 pounds and rounds it to the nearest 2.5 to give you something you can actually load, so the target weight is 237.5. The 75 percent row says 10 reps at RPE 7.5, and volume comes out at 2,375 pounds for that set. Ask the same max for 90 percent instead and you get 282.5 pounds, 4 reps, RPE 9, and 1,130 pounds of volume. Notice the target weight is rounded but the percentage row is not, so the reps and RPE always come from the percentage you typed, not from the loaded bar.
Between the rows
Type a percentage the chart does not print and the tool interpolates. At 78 percent it sits between the 75 row, 10 reps at RPE 7.5, and the 80 row, 8 reps at RPE 8, and lands on 9 reps at RPE 7.8. On a 225 pound max that is 175 pounds for 9. Reps get rounded to whole numbers, so several nearby percentages can hand you the same rep target. That is honest: the underlying precision was never finer than a rep or two anyway.
Why it drifts
Rep-max equations are population fits, and they get less accurate the further you travel from the set that anchored them. Near your true max they are decent. Down at 50 or 55 percent the spread between real people is enormous, and a 30 rep prediction is a shrug in a suit. It varies by lift and by person too. Squats usually run more reps at a given percentage than bench, and a lifter built for endurance beats the chart where a power athlete falls short. One more thing worth saying plainly: proving the estimate by grinding a set to true failure is not free. It costs you recovery, it degrades technique on the last reps, and on the big barbell lifts it is where people get hurt.
What to do with your number
Treat the rep count as a ceiling, then program a couple of reps below it. Stopping short of failure keeps nearly all the growth for a fraction of the fatigue, which lets you train hard again sooner. If you routinely beat the estimate by three reps or more, your max has moved and the input is stale, so refresh it with the one rep max estimator rather than testing a true single. If you would rather program by feel than by percentage, the RPE to percentage chart maps the same territory from the other direction, and a training max gives you a slightly conservative number to base a whole block on.
Sources: 1RM formula review, PMC
If you consistently hit more or fewer reps than predicted, update your 1RM estimate. Useful for programming AMRAP sets and sanity-checking working weights.