1RM Calculator (One-Rep Max)
Estimate your one-repetition maximum from a submaximal set using Epley, Brzycki, Lombardi, Mayhew and Wathan equations, with accuracy notes based on published validation studies.
Results
- Estimated 1RM
- 115.8 kg
- Average of six equations (5 effective reps)
- Equation spread
- 112.5 kg - 119 kg
- Lowest to highest across the six equations
- Typical accuracy range
- 104.2 kg - 127.4 kg
- Published estimates commonly fall within about ±10% of a tested 1RM
Estimated loads for 1-10 rep max sets (from 115.8 kg)
| Rep max | %1RM | Estimated load |
|---|---|---|
| 1 | 96.8% | 112.1 kg |
| 2 | 93.8% | 108.6 kg |
| 3 | 90.9% | 105.3 kg |
| 4 | 88.2% | 102.2 kg |
| 5 | 85.7% | 99.3 kg |
| 6 | 83.3% | 96.5 kg |
| 7 | 81.1% | 93.9 kg |
| 8 | 79% | 91.4 kg |
| 9 | 76.9% | 89.1 kg |
| 10 | 75% | 86.9 kg |
How it works & limitations
How the estimate works
Epley: 1RM = w x (1 + 0.0333 x r) Brzycki: 1RM = w x 36 / (37 - r) Lombardi: 1RM = w x r^0.10 O'Conner: 1RM = w x (1 + 0.025 x r) Mayhew: 1RM = (100 x w) / (52.2 + 41.9 x e^(-0.055 x r)) Wathan: 1RM = (100 x w) / (48.8 + 53.8 x e^(-0.075 x r)) w = weight lifted, r = effective reps (reps + RIR).
Which equation to trust
Validation studies report that Epley and Brzycki are among the most accurate equations for trained lifters when the set is performed to failure within about 10 repetitions. Mayhew was developed from bench-press data and is a reasonable choice for pressing work. Above 10 reps, all equations lose accuracy because fatigue changes the rep-to-load relationship.
Using RIR
If your set stopped with 2 clean reps left, you performed 5 reps at 2 RIR. Treating it as a 7-rep max gives a more conservative and usually more honest 1RM than assuming the set was to failure. A tested 1RM with a spotter remains the reference when load selection is critical.
Sources
Last updated 2026-08-13
- LeSuer, D. A., McCormick, J. H., Mayhew, J. L., Wasserstein, R. L., & Arnold, M. D. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research, 11(4), 211-213.
- Reynolds, J. M., Gordon, T. J., & Robergs, R. A. (2006). Prediction of one repetition maximum strength from multiple repetition maximum testing. Journal of Strength and Conditioning Research, 20(3), 584-592.
Estimates only. Use a directly tested 1RM with a spotter for load selection in competition or high-risk lifts, especially when the predicted value is close to a personal record.
Frequently asked questions
Which 1RM formula is most accurate?
Validation studies (e.g., LeSuer et al., 1997) show that Epley and Brzycki equations are generally the most accurate for trained lifters when the set is performed to failure within about 10 repetitions. No prediction equation replaces an actual tested 1RM, and estimates can be off by roughly 5-10% for individuals.
How many reps can I use for a reliable 1RM estimate?
Keep the set at 10 reps or fewer. Equations become progressively less accurate above 10 reps because fatigue and technique breakdown change the rep-to-load relationship.