Free Calculator
1RM Calculator — Estimated One-Rep Max
Enter the weight and reps from any set. Your estimated one-rep max is calculated instantly using six leading 1RM formulas plus a percentage table for programming.
Training percentages (from your estimated 1RM)
| % | Weight | Typical use |
|---|---|---|
| 95% | — | 2–3 RM, peaking |
| 90% | — | 3–5 RM, strength |
| 85% | — | 5–6 RM, strength |
| 80% | — | 6–8 RM, strength/hypertrophy |
| 75% | — | 8–10 RM, hypertrophy |
| 70% | — | 10–12 RM, hypertrophy |
| 65% | — | 12–15 RM, volume |
| 60% | — | Warm-up / endurance |
How is 1RM calculated?
Estimated 1RM (one-rep max) is your predicted maximum lift for a single repetition, calculated from a sub-maximal set. Each formula handles the weight × reps relationship slightly differently, but they all produce similar results in the 2–10 rep range.
The six formulas, explained
- Epley: 1RM = weight × (1 + reps / 30). The most commonly used formula.
- Brzycki: 1RM = weight × 36 / (37 − reps). Slightly more conservative than Epley above 5 reps.
- Lombardi: 1RM = weight × reps^0.10. A power-curve approach.
- O'Conner: 1RM = weight × (1 + 0.025 × reps). The most conservative of the six.
- Wathan: 1RM = (100 × weight) / (48.8 + 53.8 × e^(−0.075 × reps)). Exponential decay model.
- Mayhew: 1RM = (100 × weight) / (52.2 + 41.9 × e^(−0.055 × reps)). Designed from bench press data.
The calculator above shows all six and averages them — averaging smooths out the differences and produces a robust estimate.
How accurate is estimated 1RM?
For sets in the 2–10 rep range, all six formulas are typically within 2–5% of true 1RM. Above 10 reps, accuracy degrades rapidly because muscular endurance starts dominating over pure strength capacity — a 20-rep set tells you more about conditioning than maximal force.
For tracking progression, estimated 1RM is more useful than chasing true 1RM tests. Test 1RMs are infrequent, taxing, and carry injury risk. Estimated 1RM updates every session, so you see strength trends week-to-week without ever needing to attempt a max.
How to use 1RM in programming
Most strength programs prescribe loads as a percentage of 1RM:
- Strength block: 80–95% of 1RM, low reps (1–6), longer rest
- Hypertrophy block: 65–80% of 1RM, moderate reps (6–12), moderate rest
- Volume / metabolic block: 50–70% of 1RM, higher reps (12–20)
Use the percentage table above to translate your estimated 1RM directly into working weights for any of these zones.
Should you track 1RM over time?
Yes — but estimated, not tested. The cleanest way is to log every session, take your best set, compute estimated 1RM, and chart the trend per exercise. A flat line for 4+ weeks signals a plateau; a rising line is real strength progress.
Doing this needs nothing more than a spreadsheet and the calculator above. How to build an estimated 1RM trend covers the method in detail, including why the three-session block beats reading daily values, and how to tell a plateau from normal variation once you have the line.
Pick one formula and stay with it
The six formulas here agree closely at low rep counts and diverge as reps climb. Using different formulas on different sessions will make your trend line jump for reasons that have nothing to do with your training. Choose the one you want to track with, record which one you used, and never switch mid-series.
FAQ
What is a 1RM?
Your one-rep max — the heaviest weight you can lift for a single rep with proper form. Estimated 1RM predicts that number from a sub-maximal set without you actually having to attempt a true max.
Which formula should I use?
For most lifters, Epley or Brzycki are the standards. The calculator above shows all six and averages them — that's the most robust single number.
How often should I recalculate my 1RM?
Every session. Take your best set (highest weight × reps) and compute estimated 1RM. Tracked over weeks, this is the cleanest single number for whether a lift is progressing.
Can I trust the estimate at very high reps?
Above ~10 reps, accuracy drops. The estimate becomes more about endurance than max strength. Stick to 2–10 rep sets for reliable 1RM predictions.