One Rep Max (1RM) Calculator
Estimate your one-rep max from submaximal lifts using Epley, Brzycki, Lombardi, Mayhew, and Wathan formulas. Includes training load percentage chart.
Best accuracy with 3-10 reps performed to near-failure.
Formula Comparison
Training Load Chart
| % 1RM | Weight Lifted (lbs) | Reps Completed |
|---|---|---|
| 100% | 262.0 | 1 |
| 95% | 248.9 | 2 |
| 90% | 235.8 | 4 |
| 85% | 222.7 | 6 |
| 80% | 209.6 | 8 |
| 75% | 196.5 | 10 |
| 70% | 183.4 | 12 |
| 65% | 170.3 | 15 |
| 60% | 157.2 | 20 |
How It Works
- 1
Enter weight and reps
Enter the weight you lifted and the number of reps you completed. Select lbs or kg. For best accuracy, use a set of 3-10 reps performed to failure or near-failure.
- 2
Compare formula estimates
The calculator shows your estimated 1RM from all five formulas plus their average. If one formula consistently matches your actual max, favor that one for future programming.
- 3
Use the training load chart
The percentage chart shows how much weight to use at each intensity level. 85% of your 1RM for sets of 6, 75% for sets of 10, and so on. These ranges follow NSCA guidelines for programming.
Understanding One Rep Max Estimation
The one-rep max (1RM) is the maximum weight you can lift for a single repetition with correct form. Directly testing a true 1RM carries injury risk, especially for beginners, so prediction formulas estimate it from submaximal lifts. This calculator uses five peer-reviewed formulas: Epley (1985), Brzycki (1993), Lombardi (1989), Mayhew et al. (1992), and Wathan (1994). Each formula was derived from different populations and rep ranges. Epley and Brzycki are the most widely used. They agree closely at 5 reps (for a 225 lb bench at 5 reps, Epley predicts 262.5 lb and Brzycki predicts 253.1 lb) but diverge above 10 reps. All formulas lose accuracy beyond 10-12 repetitions because the relationship between weight and reps becomes less linear at higher rep counts, where muscular endurance dominates over maximal strength. The training load chart uses the average of all five formulas and maps it to standard NSCA percentage-based rep ranges, so you can program your working sets at the correct intensity for strength (85-95%), hypertrophy (65-85%), or endurance (below 65%).
Common pitfalls
- These formulas are validated for compound barbell lifts (squat, bench, deadlift). Isolation exercises like bicep curls or leg extensions follow different strength curves, and the formulas overestimate 1RM for them.
- Rep ranges above 10 produce increasingly unreliable estimates. At 15+ reps, muscular endurance and cardiovascular fatigue become limiting factors, not maximal strength. Keep test sets between 3-10 reps.
- The Brzycki formula is mathematically undefined at 37 reps (division by zero) and produces negative values above 37. The calculator returns 0 in this case. Stick to lower rep ranges for meaningful results.
- Training load percentages (95% = 2 reps, 90% = 4 reps) are population averages from the NSCA Essentials of Strength Training, 4th edition, Table 15.6. Individual variation is significant: some lifters can do 5 reps at 90% while others can only manage 3.
Frequently Asked Questions
Which 1RM formula is the most accurate?
Epley and Brzycki are the most validated. Brzycki tends to be slightly more conservative. For sets of 3-6 reps, both are within 5% of actual tested 1RM in most people. The average of all five formulas reduces individual formula bias.
Why do the formulas give different results?
Each formula was developed from different study populations and rep ranges. Epley uses a linear model, Brzycki uses an inverse linear model, while Mayhew and Wathan use exponential decay curves. The differences grow larger above 10 reps.
How many reps should I use for the most accurate estimate?
3-6 reps gives the best accuracy. At 1-2 reps you're so close to your max that you might as well test it directly. Above 10 reps, muscular endurance and fatigue patterns vary too much between individuals for reliable prediction.
Can I use this for any exercise?
These formulas are validated for compound barbell movements: squat, bench press, deadlift, overhead press. They overestimate 1RM for isolation exercises (curls, extensions) and machine-based movements because those exercises have different strength curves.
How do I use the training load chart?
The chart maps your estimated 1RM to working weights. For strength training (1-6 reps), use 85-100% of 1RM. For hypertrophy (6-12 reps), use 65-85%. For muscular endurance (12-20 reps), use 60-65%. These are NSCA guidelines.
How often should I retest my 1RM?
Every 4-8 weeks for intermediate lifters. Beginners gain strength fast enough that estimates shift weekly. Rather than testing a true 1RM (which is taxing), just plug in a recent heavy set of 3-5 reps.
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