One-rep max calculator
Estimate your maximum from an ordinary working set, without ever attempting a record.
Updated 26 September 2026
Past ten effective reps the estimate becomes rough. For a reliable figure, retest on a set of 3 to 8 reps.
| % of 1RM | Weight | Reps possible |
|---|---|---|
| 100 % | — | 1 |
| 95 % | — | 2 |
| 90 % | — | 4 |
| 85 % | — | 6 |
| 80 % | — | 8 |
| 75 % | — | 10 |
| 70 % | — | 12 |
| 65 % | — | 16 |
| 60 % | — | 20 |
Average of the Epley and Brzycki formulas up to 10 reps, Epley alone beyond. The percentage table is indicative: it varies by exercise and by person.
What the 1RM is for
Your 1RM, or one-rep max, is the heaviest weight you can lift once on a given exercise. It is the unit of measurement for strength, and above all the reference nearly every program uses to express its loads: “4 sets at 80%” only means something if you know what 80% is a percentage of.
The reason to estimate it rather than test it is that a maximal attempt is expensive: it fatigues the nervous system for several days and carries genuine risk on the big lifts. A well-executed set of 5 is enough to get a usable number.
How the calculation works
Two formulas have been the consensus for decades, and both rest on the same idea: the more reps you get with a weight, the further that weight is from your maximum.
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps)
They agree well on short sets and diverge past ten reps, where Brzycki runs away with itself. The calculator above averages them up to ten, then sticks to Epley — and says so when the estimate turns rough, rather than showing a falsely precise number.
The detail almost every calculator misses
These formulas assume your set went to failure. Most training sets do not — and should not. If you got 5 reps with 2 left in the tank, that weight actually corresponds to a set of 7 to failure, and your max is meaningfully higher than a naive calculator will tell you.
That is what the RIR field is for. The more you leave in reserve, the bigger the gap. Ignoring it means underestimating your strength, every single time.
What to do with the number
The percentage table gives you the matching working loads. In practice:
- Strength: 85 to 95% of 1RM, for 1 to 5 reps.
- Hypertrophy: 65 to 80%, for 6 to 12 reps.
- Muscular endurance: under 65%, past 15 reps.
One caveat though: a percentage worked out six weeks ago says nothing about how you feel today. Sleep, stress and accumulated fatigue swing performance by several percent from one day to the next. Which is why steering loads byhow the set actually felt — reps in reserve again — is more reliable than a fixed table. It is also how SETR adjusts your weights from one session to the next.
The other tools
- Barbell plate calculator — the exact loading, with the plates your gym actually has.
- Rest times between sets — how long to wait, and why.
Frequently asked questions
Should you actually test your 1RM in the gym?
Rarely, and never without a spotter and a thorough warm-up. A maximal attempt fatigues the nervous system for days and carries real risk on heavy lifts. Estimating from a set of 3 to 8 reps is accurate enough to program with, at none of the cost or danger.
At how many reps does the estimate break down?
Past ten reps every formula drifts, and they disagree with each other. That makes sense: at that point you are not limited by maximal strength but by muscular endurance and tolerance for discomfort. A set of 5 gives a far better estimate than a set of 15.
Why ask for reps in reserve?
Because a set stopped two reps short of failure does not mean the same thing as a set taken to failure. Without that information the estimate is systematically low. Most online calculators ignore it — and are therefore wrong in proportion to how much you left in the tank.
My estimated 1RM moves week to week. Is that normal?
Yes. Sleep, stress, food and accumulated fatigue swing performance by several percent day to day. Which is exactly why steering your loads by how the set actually felt (reps in reserve) beats a fixed percentage worked out six weeks ago.