One-Rep Max (1RM) Calculator + Training Loads
Estimate your one-rep max from a weight and reps using the Epley and Brzycki formulas, with a percentage table of training loads. In your browser.
Training loads
| of 1RM | kg |
|---|---|
| 95% | 108.9 |
| 90% | 103.1 |
| 85% | 97.4 |
| 80% | 91.7 |
| 75% | 85.9 |
| 70% | 80.2 |
| 65% | 74.5 |
| 60% | 68.8 |
| 55% | 63 |
| 50% | 57.3 |
🔒 Calculated in your browser. Epley & Brzycki estimates — real maxes depend on form, fatigue and the lift. Don't attempt a true max without a spotter.
Estimate your max without maxing out
Enter a weight you lifted and how many reps you managed, and the tool estimates your one-rep max (1RM) with the Epley and Brzycki formulas plus their average. It also builds a percentage table (50–95% of 1RM) so you can pick training loads for your program.
An estimate, lift safely
Rep-based estimates get less accurate as reps climb (best under about 10), and real maxes depend on form, fatigue and the lift itself. Use the numbers to program training, and never attempt a true one-rep max without a spotter or safeties. Everything runs in your browser.
The two formulas, and where they disagree
Epley is weight × (1 + reps ÷ 30). Brzycki is weight × 36 ÷ (37 − reps). They cross at exactly ten reps, where both give the same answer, and disagree either side of it. Below ten Brzycki reads lower — at one rep it returns the weight you lifted, while Epley adds 3.3% to it. Above ten the order flips and the gap widens fast, because Brzycki's denominator is shrinking: 9% apart at 15 reps, 27% at 20. The page shows both and their average rather than picking for you, because which one fits you is something only your own heavy singles can settle.
Reps are the accuracy, not the weight
A set of 3 predicts a max well. A set of 15 predicts endurance, and the number it produces is a guess about a lift you have not done. The input stops at 36 reps because Brzycki's formula divides by 37 − reps and becomes meaningless as that approaches zero — at 37 it would divide by zero outright. If you want a usable estimate, test with a weight you can move 3 to 6 times with the last rep genuinely hard.
Frequently asked questions
How is one-rep max calculated?
From a submaximal set: Epley = weight × (1 + reps/30); Brzycki = weight × 36 ÷ (37 − reps). 100 kg × 5 reps is about 113–117 kg.
How accurate are 1RM estimates?
Good for low reps (roughly under 10) and rougher above that. They’re a training guide — form and fatigue affect a real max.
Which formula should I use?
Near ten reps it does not matter at all — the two formulas meet there. Below ten, Brzycki is the conservative one; above ten, Epley is, and by twenty reps they are 27% apart. Most people take the average, which is what the third figure shows, and then correct it against a real heavy single once they have one.
Why does it stop at 36 reps?
Brzycki divides by 37 minus your rep count, so at 37 reps it divides by zero and just below that it produces enormous numbers. 36 is only the last input before that division, not a usable one: at 36 reps Brzycki returns 36 times the weight you lifted. Estimates are worth trusting under about 10 reps; past that, read them as a rough guide.
Is the estimate a weight I should attempt?
No. It is arithmetic on one set, with nothing in it about your form, your fatigue that day, or whether you have a spotter. Treat it as a starting point for programming percentages, not as a target to walk up to the bar and try.