How to use the one rep max calculator
- Choose kilograms or pounds.
- Enter the weight lifted in a recent hard set.
- Enter the reps completed with good form, up to 12. The closer the set was to failure, the better the estimate.
- Read your estimated one-rep max (1RM), each formula's result, and the table of training loads.
The one-rep max formulas
Each formula turns a weight lifted for several reps into an estimated single-rep max. The calculator shows all five and uses their average as the main result.
They were fitted to different groups of lifters and exercises, so they disagree a little, especially at higher reps. Epley and Wathan tend to give higher estimates, while Brzycki and O'Conner give lower ones. Averaging them smooths out the differences. With exactly one rep, there is nothing to estimate: your 1RM is the weight you lifted.
Worked example
The calculator's defaults are 100 kg for 5 reps:
| Formula | Working | 1RM |
|---|---|---|
| Epley | 100 × (1 + 5 ÷ 30) | 116.7 kg |
| Brzycki | 100 × 36 ÷ 32 | 112.5 kg |
| Lombardi | 100 × 5^0.10 | 117.5 kg |
| O'Conner | 100 × (1 + 0.125) | 112.5 kg |
| Wathan | 100 × 100 ÷ (48.8 + 53.8 × e^(−0.375)) | 116.6 kg |
The average is 575.7 ÷ 5 = 115.1 kg. From that, 80% of 1RM is 92.1 kg (92.5 kg on the bar) and 70% is 80.6 kg (80 kg). In pounds, 225 lb for 8 reps gives an average of 279.7 lb.
Using percentages of your 1RM
Strength programs often prescribe loads as a percentage of 1RM. The table in the calculator lists 50% to 95% and the reps you could roughly manage at each load, using the Epley equation in reverse:
| % of 1RM | Approximate reps to failure | Typical use |
|---|---|---|
| 90–95% | 2–3 | Maximal strength, low volume |
| 80–85% | 5–8 | Strength |
| 70–75% | 10–13 | Muscle size (hypertrophy) |
| 50–65% | 16–30 | Technique, warm-ups, muscular endurance |
You don't need to train to failure. Most sets end with one to three reps "in the tank", so pick a load a little lighter than the table suggests for the reps you plan to do.
Limits of 1RM estimates
The formulas are most accurate for sets of about 2 to 10 reps on big barbell lifts such as the squat, bench press and deadlift. They are less reliable for machines, single-joint exercises, beginners, and sets over 10 to 12 reps. Muscular endurance differs between people: one lifter may manage 8 reps at 80% and another only 5. Treat the result as a starting point and adjust it from how your training sets feel.
Testing a true 1RM carries more risk than a normal set. Warm up well, use a spotter or safety bars, and stop if your form breaks down. If you have high blood pressure, a heart condition or a joint injury, talk to your doctor before heavy lifting.
Frequently asked questions
Which 1RM formula is most accurate?
None is best for everyone. Studies comparing them find each one works well in some lifts and groups and less well in others. Epley and Brzycki are the most widely used, and the average of several formulas is a sensible middle estimate.
How many reps should I use for the estimate?
A hard set of 3 to 6 reps gives the most reliable estimate. Sets of 10 or more depend more on muscular endurance than on maximal strength, so the estimate drifts further from your real max.
Can I use this for any exercise?
It works best for compound free-weight lifts. For machines, isolation exercises such as curls, and bodyweight movements, the formulas are less accurate, so use the result loosely.
How often should I retest my max?
Most lifters re-estimate every four to eight weeks, or at the end of a training block. You can use any hard set from your normal training, so you rarely need to attempt a true single-rep max.
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Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.