How this instrument works
A true one-rep max on the bench press means loading a bar to the absolute heaviest weight you can press exactly once, which carries real risk on this particular lift: unlike a squat or deadlift, a missed bench press can pin you under the bar with limited ways to bail out safely without a spotter or safety arms. Estimating instead — using a lighter, safer set you've already completed — sidesteps that risk while still giving programming a usable number.
This instrument uses the Epley formula, 1RM = weight x (1 + reps/30), attributed to strength coach Boyd Epley's 1985 poundage chart and one of the two most widely used one-rep-max estimators in strength training. It works from any sub-maximal set: enter what you lifted and how many clean reps you completed, and it projects what a single all-out rep at that same effort level would likely be.
The formula's accuracy has limits worth knowing before trusting the number too far. Research on estimating 1RM from multi-rep testing has found that predictions from moderate rep ranges track true one-rep performance closely, but accuracy declines as the rep count climbs — a set of 15 or 20 reps sits much further from a true single than a set of 3 to 6, so the estimate drifts further from reality the higher the rep count you feed it.
- Enter Weight lifted — the bar weight (plus bar, if you're counting total load) from a bench set you completed with good form.
- Enter Repetitions completed — how many clean reps you got in that set, ideally at or close to failure.
- Read Estimated one-rep max — the projected single-rep weight the Epley formula estimates from that set.
- Keep the rep count under about 10 for the most reliable estimate; higher-rep sets push the formula further from its accurate range.
- Re-test with a fresh set every few weeks as strength changes — a single old data point becomes a stale estimate quickly.
Worked example — 185 lb for 5 reps
Enter 185 lb as the weight lifted and 5 as the reps completed. The Epley formula gives 1RM = 185 x (1 + 5/30) = 185 x 1.16667 = 215.8333... lb — an estimated one-rep max just under 216 lb from a set that never went anywhere near a true single.
That estimate sits roughly 17% above the 185 lb actually lifted, which matches the formula's built-in logic: every rep beyond the first is assumed to represent about 1/30th of extra one-rep capacity, so a 5-rep set projects a meaningfully heavier single than the weight on the bar.
Questions
How accurate is the Epley formula for bench press specifically?
It's a solid estimate within its intended range — roughly 2 to 10 reps — but it's still an estimate, not a measurement. Research comparing predicted and actual one-rep performance across bench press, squat and deadlift has found correlations with true 1RM are consistently high, though the exact predicted number can run a few percent off in either direction depending on the individual and the exercise, with accuracy declining further outside the low-rep range.
Why does the formula divide reps by 30?
It's Epley's chosen scaling constant: each additional rep beyond the first is treated as roughly 1/30th, or about 3.3%, of extra one-rep strength capacity. That constant was fit to observed lifting data rather than derived from a physiological law, which is why it works well as a general-purpose approximation but shouldn't be treated as an exact physics equation.
Is the formula more or less accurate for bench press than for squat or deadlift?
Prediction accuracy varies by lift in the research literature — multi-rep-based 1RM predictions have generally performed differently across the bench press, squat and deadlift, since each lift has a different fatigue profile and technical demand as reps accumulate. That variation is exactly why programming should treat any Epley estimate as a useful planning number rather than a certified maximum.
Is it safe to just attempt a true 1RM on bench press instead of estimating?
Only with proper safety equipment and supervision — a spotter, safety arms/pins set to the right height, or both — since a failed rep can trap the weight on your chest with no easy way out. Estimating from a lighter, safer set avoids that risk entirely, which is exactly why formula-based 1RM estimates are standard practice in strength training programs.
How is this different from the general one-rep-max calculator on this site?
Same Epley formula and same math — the difference is framing. This page is scoped specifically to the bench press and its particular safety considerations around attempting a true single without a spotter. The site's general one-rep-max calculator applies the identical formula to any barbell lift, including ones like the squat and deadlift where the failure-mode risks differ.
How often should I recalculate my estimated 1RM?
Every few weeks of consistent training is reasonable, since strength shifts gradually rather than overnight. Recalculating from a recent set — rather than reusing a number from months ago — keeps any programming built on top of the estimate (percentage-based training max calculators, for instance) aligned with your current strength.