One Rep Max (1RM) Calculator
Enter the weight you lifted and the number of clean reps you completed, and this calculator estimates your one-rep max (1RM) — the most you could lift for a single repetition. It reports both the Epley and Brzycki estimates and builds a percentage-of-1RM table so you can plan training loads for strength, hypertrophy, and technique work. Estimates are most reliable for sets of about 10 reps or fewer.
Your set
Formula
Both estimates are shown; the selected one drives the table below.
Estimated one-rep max (epley)
116.67 kg
from 100.00 kg × 5 reps
Epley
116.67 kg
Brzycki
112.50 kg
Percentage-of-1RM training table
Working loads by intensity
Compare scenarios
Run the same calculation with two or three input sets side by side. Differences are highlighted; every number comes from the same tested formula as the calculator above.
| Input | Scenario A | Scenario B |
|---|---|---|
| Weight | ||
| Reps | ||
| Formula |
How it works
Your one-rep max is estimated from a submaximal set using a rep-to-max formula. The default, Epley, is 1RM = weight × (1 + reps/30): so a 100 kg set of 5 predicts 100 × (1 + 5/30) = 116.67 kg. At a single rep every formula collapses to the weight itself, because you are already lifting your max. These equations were fit to real lifting data and assume the set was taken close to muscular failure with strict form — a set left with reps in reserve will under-predict your true max.
The Brzycki formula, 1RM = weight × 36 / (37 − reps), is offered alongside Epley as a cross-check. The two agree closely at low reps and diverge as reps climb: Brzycki tends to read lower than Epley in the higher-rep range. That is why this tool caps reps at 36 — the Brzycki denominator (37 − reps) collapses toward zero and the estimate becomes meaningless as it approaches 37 reps. Seeing both numbers gives you a sensible range rather than a single false-precision figure.
Once the 1RM is estimated, the calculator multiplies it by a ladder of standard training intensities — 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, and 100% — to produce a load table. Coaches use these percentages to program: roughly 50–70% for technique and hypertrophy volume, 75–85% for strength work, and 90%+ for peaking and maximal singles. The table lets you turn one tested set into concrete working weights across a whole training block.
Frequently asked questions
How accurate is a one-rep max estimate?+
For sets of about 2 to 10 reps taken close to failure with strict form, rep-based 1RM formulas are usually within a few percent of a directly tested max, which is good enough for programming. Accuracy drops noticeably above roughly 10 reps: at high rep counts, fatigue, breathing, and pacing dominate, so the formulas increasingly over- or under-estimate your true single. If you need an exact number — for a competition attempt, for example — nothing replaces a properly warmed-up, supervised max test. Treat the estimate as a training guide, not a guarantee.
Should I use the Epley or the Brzycki formula?+
Neither is universally 'correct' — both are population-level regressions fit to lifting data, and they trade blows depending on the lift and the rep range. At low reps they land within a kilogram or two of each other. As reps rise, Epley tends to predict a slightly higher 1RM and Brzycki a slightly lower one, so reading them together gives you a realistic range. A practical approach: use the lower of the two when picking an opener or a heavy single, and the higher when you just need a ballpark for percentage-based volume work.
Is it safe to test or lift near my one-rep max?+
This calculator is a training tool, not medical or coaching advice. Lifting near your maximum carries real injury risk and should only be attempted after a thorough warm-up, with sound technique, appropriate spotters or safety pins, and ideally the guidance of a qualified coach. Beginners in particular should build a base of technique and volume before chasing maximal loads, and anyone with an injury, a medical condition, or who is new to resistance training should consult a physician or certified strength professional before testing limits.