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One
rep max calculator
Enter a set you have actually done. We show five formulas, the spread between them, and the percentage table you need to programme from the result.
Why estimate instead of test
A true one rep max attempt costs a great deal for a single data point. It needs a spotter, a full warm-up, a fresh nervous system, and it leaves you fatigued for days. It also carries the highest injury risk of anything you will do in a gym, because maximal loads punish small technique errors that submaximal loads forgive.
A hard set of three to five gives you a number within a few percent, costs one set, and can be taken during normal training. For programming purposes that is the same information.
Accuracy falls off a cliff after ten reps
Rep-max formulas assume a fairly consistent relationship between load and repetitions. That relationship holds well at low reps and falls apart at high ones, because how many reps you can do at 60 percent of your max depends on your muscle fibre composition and conditioning far more than your peak strength does.
Two people with an identical 140 kg max might manage twelve and twenty reps at 100 kg. No formula can distinguish them. That is why the spread between formulas on this page widens as you enter more reps — it is showing you the estimate getting less trustworthy.
Using the percentages
The table is the practical output. Most strength programmes are written as percentages of a max: five sets of three at 85 percent, or five at 75.
Two cautions. Percentages assume your max is current — recalculate every six to eight weeks rather than working from a number you set last year. And the relationship is lift-specific, so a percentage that feels right on a squat may be brutal on a deadlift, which fatigues far more per set.
The estimate is a ceiling, not a promise
Expect your first genuine single to land slightly below the calculated figure. Handling a maximal load is a skill — bracing hard enough, committing to the descent, staying tight when it feels heavy — and a set of five does not train it.
Lifters who train regularly near their max close that gap. Lifters who live in the eight to twelve rep range often find the shortfall is five percent or more, and that is a training-exposure problem rather than a calculator error.
Common questions
How do you calculate your one rep max?
Take a weight you can lift for a known number of reps and run it through a rep-max formula. Epley is the most common: 1RM = weight × (1 + reps ÷ 30). At five reps with 100 kg that gives 117 kg. Accuracy is good up to about five reps and degrades quickly beyond ten.
How accurate are one rep max calculators?
Within a few percent if your test set was five reps or fewer and taken close to failure. Above ten reps the estimate depends heavily on your muscle fibre make-up and work capacity, and different formulas can disagree by ten percent or more — which is why this page shows a range rather than one number.
Which one rep max formula is best?
Epley and Brzycki are the two most used and agree closely at low reps. Brzycki reads slightly lower at higher reps and breaks down entirely at 37 reps, where its denominator hits zero. For practical purposes, take the spread from several formulas as your estimate.
Should I actually test my one rep max?
Rarely. A true max attempt is fatiguing, needs a spotter and carries more injury risk than the information is usually worth. Estimating from a hard set of three to five gives you a number accurate enough to programme with, at a fraction of the cost.
How many reps should I use for the estimate?
Three to five, taken to within a rep or two of failure. Fewer than three and a single grinding rep skews it; more than eight and the estimate becomes a guess about your endurance rather than your strength.
Why is my calculated max higher than what I can actually lift?
Because a true single demands technique, bracing and psychological commitment that a set of five does not train. Formulas describe the physics; they cannot account for a lifter who has never held a maximal load. Expect a first real attempt to fall a few percent short of the estimate.