Estimate Your One-Repetition Maximum (1RM) maximum (1RM) using the Epley formula.
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One-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. Testing a true 1RM directly carries injury risk, so most lifters estimate it using a formula like Epley's, based on a lighter weight lifted for multiple reps. This estimate is commonly used to plan training percentages for strength programs. One-rep max (1RM) — the heaviest weight someone can lift once with proper form — is foundational in strength training for calculating training percentages and tracking progress. Lifting an actual max carries real injury risk, especially for beginners, so trainers developed formulas like Epley's and Brzycki's that estimate 1RM from a lighter, safer lift of several reps, based on a fairly predictable relationship between reps performed and percentage of max. Because these prediction formulas were built from data on trained lifters performing standard barbell exercises, accuracy tends to drop somewhat for less common movements, beginners still learning proper form, or anyone whose true strength curve differs from the population average the formula was originally built from.
One-rep max (1RM) — the heaviest weight someone can lift for a single complete repetition with proper form — is a foundational number in strength training, used to calculate training percentages for programs, track strength progress over time, and compare relative strength across lifters of different sizes. Testing a true 1RM directly requires a maximal, often risky attempt, which is why estimation formulas based on higher-repetition, lower-risk sets became standard practice in strength and conditioning.
This calculator uses the Epley formula (1985), one of several validated prediction equations alongside Brzycki (1993) and Lombardi (1989), among others — each formula was derived from different research populations and rep ranges, which is why they produce slightly different estimates for the same input, particularly as the number of reps performed increases. All of these formulas share the same underlying assumption: that the relationship between weight lifted and repetitions performed follows a predictable pattern, at least within a reasonable rep range.
Accuracy degrades meaningfully outside that reasonable range — estimates based on 1-5 reps tend to be quite reliable, since they're close to an actual max effort, while estimates extrapolated from higher rep sets (10+ reps) become progressively less accurate, because muscular endurance and strength don't scale together in a perfectly linear way for every lifter. This is one reason strength coaches generally recommend testing or estimating 1RM using sets in the 3-6 rep range rather than extrapolating from a set of 15 or 20.
Beyond programming training percentages, tracking estimated 1RM over months provides a much clearer strength progress metric than simply tracking the weight used for a fixed number of reps, since it normalizes for any changes in rep count between sessions — a genuinely useful number for anyone following a structured strength program, provided it's understood as a well-informed estimate rather than a verified maximal lift.
It's a reliable estimate for most rep ranges under about 10, though accuracy decreases at very high rep counts.
Formulas like Epley's and Brzycki's are most accurate with fewer than about 10 reps — accuracy drops noticeably at higher rep counts, since the rep-to-strength relationship becomes less linear at lighter loads.
Only with proper form, a spotter, and adequate warm-up — many lifters prefer to rely on estimates for everyday programming.