What is a one-rep max (1RM)?
Your one-rep max, or 1RM, is the heaviest weight you can lift for a single clean repetition of a given exercise: back squat, bench press, deadlift, and so on. It is the standard yardstick for strength and the anchor for most training programs, since routines are usually written as a percentage of your max, for example 5 sets of 5 at 80 % of 1RM.
Testing a true 1RM by piling on plates until you can barely move the bar is risky: form breaks down under maximal loads and injury risk climbs. This calculator instead estimates your 1RM from an ordinary work set. You enter the weight you lifted and how many reps you managed, and it returns your approximate max without the danger of an all-out attempt.
How to use the calculator
- Enter the weight lifted in your set, choosing kg or lb in the unit selector.
- Enter how many reps you completed, from 1 to 15. Fewer reps give a more reliable estimate.
- Read your 1RM: the tool shows two formulas plus their average.
- Use the percentage table to plan your working sets.
At 1 rep the 1RM is simply the weight itself, because that set already was your max. Accuracy is best between 2 and 8 reps; above 10 reps the formulas tend to overestimate.
The formulas: Epley and Brzycki
The calculator uses the two most widely cited strength formulas. With w = weight and r = reps:
- Epley:
1RM = w × (1 + r / 30) - Brzycki:
1RM = w × 36 / (37 − r)
The two agree almost exactly at 10 reps and drift apart at the edges, with Epley reading a little higher at high rep counts. Showing both and their average gives you a realistic range rather than one misleadingly precise number.
Worked example
Say you bench press 100 kg for 5 clean reps:
- Epley: 100 × (1 + 5 / 30) = 100 × 1.1667 = 116.7 kg
- Brzycki: 100 × 36 / (37 − 5) = 3600 / 32 = 112.5 kg
- Average: (116.7 + 112.5) / 2 = 114.6 kg
Your estimated 1RM is about 114.6 kg. From that number the working weights fall out:
| % of 1RM | Approx. reps | Weight |
|---|---|---|
| 95 % | 2–3 | 108.9 kg |
| 90 % | 4 | 103.1 kg |
| 85 % | 6 | 97.4 kg |
| 80 % | 8 | 91.7 kg |
| 75 % | 10 | 85.9 kg |
| 70 % | 12 | 80.2 kg |
So if your program calls for 5 reps at 85 %, you would load roughly 97 kg.
Frequently asked questions
Which formula is more accurate, Epley or Brzycki?
Neither is perfect; both are statistical models. Brzycki usually fits better below 10 reps and Epley at higher rep counts. That is why the tool reports the average of the two, which in practice trims the error compared with relying on a single formula.
How many reps give a trustworthy estimate?
The sweet spot is a set of 2 to 6 reps taken close to failure with solid technique. The more reps you grind out, the more muscular endurance rather than maximal strength drives the set, so the calculated 1RM loses accuracy past 10 to 12 reps.
Should I test my real 1RM in the gym?
Only if you are experienced, technically sound, and ideally have a spotter. For most lifters, estimating the 1RM from a submaximal set is safer and good enough for programming. This figure is a guide, not a substitute for the judgment of a qualified coach or healthcare professional.
Does it work for every exercise?
It works best on multi-joint barbell lifts such as the squat, press, deadlift, and row. On isolation moves or dumbbell work the link between reps and maximal strength is looser, so treat the result as a rough guide.