One Rep Max Calculator
Estimate the maximum weight you could lift for a single repetition based on a lighter multi-rep set. Used by powerlifters and gym-goers to set training zones and track strength progress.
About this calculator
The One Rep Max (1RM) is the gold standard measure of maximal strength for a given exercise. This calculator uses the Epley formula: 1RM = weight / (1.0278 − 0.0278 × reps). You perform a submaximal set — say, 5 reps at 80 kg — and the formula back-calculates your theoretical single-rep ceiling. The formula is most accurate when the rep count stays between 2 and 10; beyond 10 reps, fatigue factors distort the estimate. Knowing your 1RM lets you prescribe training intensities as percentages (e.g., 75% of 1RM for hypertrophy work) and compare strength across body weights when combined with a Wilks score.
How to use
Suppose you bench-pressed 90 kg for 6 reps. Plug in weight = 90 and reps = 6. The formula gives: 1RM = 90 / (1.0278 − 0.0278 × 6) = 90 / (1.0278 − 0.1668) = 90 / 0.861 ≈ 104.5 kg. That means your estimated one-rep max is about 104.5 kg. You could then set your 80% training weight at roughly 83.6 kg for hypertrophy blocks, or 90% at ~94 kg for strength-focused sessions.
Frequently asked questions
How accurate is the Epley one rep max formula compared to actually testing your 1RM?
The Epley formula is generally within 5–10% of a true tested 1RM when reps are kept between 2 and 10. Accuracy drops noticeably above 10 reps because muscular endurance, not raw strength, becomes the limiting factor. Individual differences in muscle fiber composition also introduce variation. For programming purposes the estimate is reliable enough, but serious competitive lifters should periodically perform a true max attempt under safe conditions.
What rep range should I use to get the most accurate one rep max estimate?
Using 3–6 reps produces the most reliable estimate with the Epley formula. At this range you are close enough to maximal effort that strength — rather than endurance — limits the set, keeping the formula's assumptions valid. Single or double rep attempts can be used directly (they are your actual near-max), while sets above 8–10 reps tend to overestimate or underestimate 1RM depending on the individual's endurance capacity.
How do I use my one rep max to structure a strength training program?
Once you have your 1RM, assign training loads as a percentage of that number. Typical guidelines suggest 85–95% of 1RM for maximal strength (1–3 reps), 67–85% for hypertrophy (6–12 reps), and 50–67% for muscular endurance (15+ reps). Reassess your 1RM every 4–8 weeks as you get stronger so your percentages stay accurate. Many periodization models such as 5/3/1 and Prilepin's chart are built entirely around 1RM percentages.