Your one rep max, without testing it.
Enter a set you've already done. You get an estimated 1RM from four published formulas, and the percentage chart underneath it — which is the part you'll actually use to load the bar.
The four equations
All of them do the same thing: extrapolate from a submaximal set to a single, on the observation that reps and load trade off in a roughly predictable way.
Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)
Lombardi (1989): 1RM = weight × reps^0.10
O'Conner (1989): 1RM = weight × (1 + reps ÷ 40)
At three to six reps they land within a couple of percent of each other. At ten or more they scatter, and the scatter is not random — it reflects that people differ in how many reps they can do at a given percentage. Some athletes hit twelve at 75% of their max; others manage eight. Neither is wrong.
What the percentage chart is for
Almost nobody needs a one rep max as a number. What they need is a way to answer “what should I put on the bar today” when a program says 4 sets of 6 at 85%. That is what the chart does.
One caveat worth stating plainly: the estimate is only as good as the set you fed it. A set with four reps left in the tank produces an estimate of nothing at all. If you stopped because the set felt hard rather than because the bar slowed down, the number above is optimistic — and the percentages built on it will be too heavy.
Questions people ask
How do I calculate my one rep max without testing it?
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Take a set close to failure at a weight you can manage for three to six reps, enter the weight and the reps, and the formulas do the rest. That is safer than a true max attempt, repeatable, and accurate enough to program from — which is all a 1RM is really for.
Which 1RM formula is most accurate?
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None of them consistently. Epley and Brzycki are the two most used and they agree closely at low reps, then diverge as reps climb — Brzycki reads lower at high reps, Epley higher. This page averages four published equations and shows all of them, because picking one and presenting it as the answer would imply a precision none of them has.
Why cap it at 12 reps?
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Because beyond that the estimate stops meaning much. A 15-rep set is largely a test of muscular endurance and work capacity, and the relationship between that and a true single is weak and highly individual. Brzycki's formula is mathematically undefined at 37 reps and unreliable long before it.
How often should I re-test?
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Every four to six weeks. Your 1RM does not change session to session, and re-estimating weekly produces noise you will be tempted to act on. Run a block of training, then re-estimate and update the percentages.
Should beginners use a 1RM at all?
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Not really. In your first six months, strength rises fast enough that any estimate is out of date within a fortnight, and technique is still changing under load. Beginners get more from adding a rep or a small amount of weight each session than from training off percentages of a moving target.
Related calculators
A number is a starting point, not a plan.
This calculator can tell you where you are. It cannot watch your form, adjust when your knee flares up, or keep you consistent in week six. If you want that part, we run a private studio in Kharadi and the first session is free.
This tool provides general fitness and nutrition information for healthy adults aged 18 and over. It is not medical advice, diagnosis or treatment. Speak to a doctor before starting any new exercise or nutrition programme, particularly if you have a health condition, are pregnant or post-partum, or have a history of disordered eating.