One Rep Max Calculator
Estimate your one-rep max from any set using seven published formulas, with a training-load table for every rep target.
Enter the weight and the number of clean reps — your estimated one-rep max updates as you type.
- Estimated 1RM
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- Formula used
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- Your set as % of 1RM
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- Estimate spread
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Training loads
| Reps | % of 1RM | Load (kg) |
|---|
All seven formulas
Every published estimator applied to the same set. They usually agree within a few percent — a wide spread means the rep count is high and the estimate is shakier.
| Formula | Estimated 1RM (kg) | Equation |
|---|
These are statistical estimates from submaximal sets, not a measurement — treat them as a starting point for programming, not a target to chase. They are general fitness information and not medical advice. Warm up properly, use a spotter or safety pins for heavy singles, and talk to a coach or health professional before testing a true max.
How it works
A one-rep max (1RM) is the heaviest weight you could lift once with good form. Rather than
actually attempting it, you can estimate it from a submaximal set: the more reps you get with
a given weight, the higher your true max must be. This calculator applies seven published
equations to your set. The default is Epley
(1RM = w × (1 + r ÷ 30)), the most widely used; Brzycki
(1RM = w × 36 ÷ (37 − r)) is the other common one and tends to read a little
lower. Lombardi (w × r^0.10), O'Conner (w × (1 + 0.025r)), Lander,
Mayhew and Wathan round out the set, and the "Average" option takes the mean of all seven.
At exactly one rep every formula simply returns the weight you lifted, because that
is your max.
The training-load table inverts whichever formula you selected, so the rep count you entered always maps back to the weight you actually lifted. Accuracy is best from 2–6 reps; past about ten reps endurance and technique start to dominate and every estimator drifts, which is why the calculator warns you above ten and stops at fifteen. The unit selector is only a label — the maths is scale-free, so 100 kg for 5 reps and 100 lb for 5 reps give the same percentages. Everything is computed in your browser with plain JavaScript: your numbers are never uploaded or stored, and there are no ads or sign-ups.
Frequently asked questions
How do you calculate your one rep max?
You estimate it from a submaximal set instead of attempting a true single. The most common equation is Epley: 1RM = weight × (1 + reps ÷ 30), so 100 kg for 5 reps gives 100 × (1 + 5/30) = 116.7 kg. Brzycki is the other standard: 1RM = weight × 36 ÷ (37 − reps), which gives 112.5 kg for the same set. This calculator runs seven published formulas — Epley, Brzycki, Lombardi, O'Conner, Lander, Mayhew and Wathan — side by side so you can see the spread rather than trusting one number. At exactly one rep every formula returns the weight you lifted, because that already is your max.
Is Epley or Brzycki more accurate?
Neither is universally better; they are regression fits to different populations. Brzycki reads lower than Epley at higher rep counts and is often preferred for sets under about 10 reps, while Epley is the most widely used default and tends to suit stronger, more experienced lifters. They agree closely at 2–3 reps and diverge as reps climb — at 10 reps Epley is roughly 4% higher than Brzycki. If you are unsure, use the "Average of all seven" option and read the estimate spread shown next to it: a tight spread means the formulas agree and the number is trustworthy.
How many reps is 80% of your one rep max?
Most lifters manage about 8 reps at 80% of their 1RM, which is why 8 × 80% is such a common hypertrophy prescription. The usual landmarks are roughly 95% for 2 reps, 90% for 3–4, 85% for 6, 80% for 8 and 75% for 10. This calculator does not use a generic chart — it inverts whichever formula you selected, so the rep count you entered maps back exactly to the weight you actually lifted, and every other row is consistent with it. Accuracy is best between 2 and 6 reps; beyond about 10 reps endurance and technique dominate and all estimates drift.