One rep max (1RM) calculator
Enter a weight and the reps you completed. We estimate your one-rep max with five validated formulas, average them, and give you training loads from 50% to 100%.
Gymex updates your estimated 1RM automatically after every logged set and flags new PRs.
Get the appHow the 1RM calculator works
Your one-rep max (1RM) is the heaviest weight you can lift for a single clean rep. Testing it directly is tiring and carries more risk, so most lifters estimate it from a heavier set of 2–10 reps. Each formula maps "weight × reps" to a predicted single:
- Epley: 1RM = weight × (1 + reps ÷ 30). The most widely used formula, and reliable from about 3 to 10 reps.
- Brzycki: 1RM = weight × 36 ÷ (37 − reps). It reads slightly lower than Epley at higher reps.
- Lombardi: 1RM = weight × reps0.10.
- O'Conner: 1RM = weight × (1 + 0.025 × reps).
- Wathan: 1RM = 100 × weight ÷ (48.8 + 53.8 × e−0.075 × reps).
We show every result and their average. If the formulas disagree a lot, the set probably had too many reps to predict a single well.
Rep max chart
The same maths works backwards: if you know your 1RM, this is roughly what you can lift for a given number of reps.
| Reps completed | Epley % of 1RM | Brzycki % of 1RM | Example: 1RM 100 kg |
|---|---|---|---|
| 1 | 100.0% | 100.0% | ~100.0 kg |
| 2 | 93.8% | 97.2% | ~95.5 kg |
| 3 | 90.9% | 94.4% | ~92.7 kg |
| 4 | 88.2% | 91.7% | ~90.0 kg |
| 5 | 85.7% | 88.9% | ~87.3 kg |
| 6 | 83.3% | 86.1% | ~84.7 kg |
| 8 | 78.9% | 80.6% | ~79.8 kg |
| 10 | 75.0% | 75.0% | ~75.0 kg |
| 12 | 71.4% | 69.4% | ~70.4 kg |
Getting an accurate estimate
- Use a hard set of 3–6 reps. Accuracy drops fast above 10 reps, because muscular endurance starts to matter more than maximal strength.
- Count only clean reps. No bounces, half reps or spotter help.
- Use a set close to failure. A set stopped 3 reps short underestimates your max. To account for that, use our RPE calculator, which adjusts for reps left in the tank.
- Track the trend. One estimate is noisy. A rolling e1RM over weeks shows whether your program is working. See how to break a strength plateau.
Using your 1RM to program training
Most strength programs prescribe loads as a percentage of 1RM: roughly 85–95% for heavy triples and singles, 70–85% for strength-hypertrophy work, and 60–75% for higher-rep volume. Use the percentage table in the calculator above to turn your estimate into working weights. Then let your performance on the day, measured with Reps in Reserve, fine-tune the load.
Frequently asked questions
What is the most accurate 1RM formula?
No single formula is best for everyone. Epley and Brzycki are the most widely used and agree closely between about 3 and 6 reps. Averaging several formulas, as this calculator does, smooths out individual bias.
How many reps should I use to estimate my 1RM?
Use a hard set of 3 to 6 reps for the best estimate. Predictions from sets of more than 10 reps become much less reliable.
Is it safe to test a true 1RM?
A true max test is reasonably safe for experienced lifters with good technique, a proper warm-up and a spotter or safety bars. Beginners usually get a safer and similarly useful number from an estimated 1RM.
Does the 1RM calculator work in pounds?
Yes. Switch the units to lb and every result and percentage is shown in pounds. The maths is the same in kg and lb.
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More free strength tools
- RPE & RIR calculator: Turn any set at a given RPE into an e1RM, then find the load for your next target reps and RPE.
- Barbell plate calculator: Which plates go on each side of the bar for any target weight, in kg or lb.
- DOTS & IPF GL calculator: Score your squat, bench and deadlift total against your bodyweight with DOTS and IPF GL points.
- TDEE & macro calculator: Estimate your daily calories and protein, fat and carb targets for cutting, maintaining or building muscle.
- 5/3/1 calculator: Your training max and every set of a full 5/3/1 cycle, rounded to the plates you have.
- Warm-up set calculator: A ramp of warm-up sets from the empty bar to your working weight, with sensible reps.
- Body fat calculator: Estimate body fat with the U.S. Navy tape-measure method, plus lean and fat mass.
These calculators give estimates for healthy adults. They are not medical advice. If you have an injury or a health condition, speak to a qualified professional before changing your training or diet.