The short answer
Your one-rep max (1RM) is the heaviest weight you could lift once with good form. This calculator estimates it from a lighter set of 1 to 12 reps, using four published formulas: Epley, Brzycki, Lombardi and O'Conner. It shows the average, the range and a training percentage table. Estimates are most accurate for sets of 10 reps or fewer.
Formulas and sources are named on this page. How we calculate.
How this is calculated
Each formula predicts the one-rep max from the weight lifted and the reps completed. They were fitted to different groups of lifters, so they disagree by a few percent. Averaging four of them smooths out the quirks of any one equation.
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Lombardi: 1RM = weight × reps0.10
O'Conner: 1RM = weight × (1 + 0.025 × reps)
Estimate = average of the four
Worked example
You lift 100 kg for 5 reps.
- Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg
- Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg
- Lombardi: 100 × 50.10 = 117.5 kg
- O'Conner: 100 × (1 + 0.025 × 5) = 112.5 kg
- Average = (116.7 + 112.5 + 117.5 + 112.5) ÷ 4 = about 114.8 kg, and the range is 112.5 to 117.5 kg.
The percentage table
The table of training weights uses your average estimate. The approximate maximum reps at each percentage come from rearranging the Brzycki equation: reps = 37 − 36 × (percentage ÷ 100). It is a rough guide, since two lifters with the same 1RM can differ a lot in how many reps they can do at 70 or 80%.
Why accuracy falls with more reps
Every formula extrapolates from your set to a single maximal rep. The further the set is from one rep, the larger the error, and fatigue, breathing and the type of lift matter more. Studies comparing equations find that the best one differs by lift and by person, so no single formula is best. That is why this calculator limits reps to 12 and warns above 10.
Percentage of 1RM and approximate reps
A rough guide to how many reps you can do at a percentage of your one-rep max, and how that weight is commonly used in training.
Training percentages| % of 1RM | Approx. max reps | Typical use |
|---|
| 100% | 1 | A true one-rep max |
| 95% | 3 | Heavy singles and low-rep strength work |
| 90% | 5 | Strength sets of about 3 to 5 reps |
| 85% | 6 | Strength sets of about 5 to 6 reps |
| 80% | 8 | Strength and size sets of about 6 to 8 reps |
| 75% | 10 | Size and strength sets of about 8 to 10 reps |
| 70% | 12 | Size sets of about 10 to 12 reps |
| 65% | 14 | Higher-rep size and endurance work |
| 60% | 15 | Endurance and technique work |
| 55% | 17 | Warm-ups and light technique work |
| 50% | 19 | Warm-ups and light technique work |
Reps are approximate and vary by lift and by person. The calculator above shows the weights for your own estimate.
Frequently asked questions
What is a one-rep max?
It is the heaviest weight you can lift for one complete repetition with good form on a given exercise. Lifters use it to set training weights as percentages, and to track strength over time.
How accurate is a one-rep max calculator?
It is an estimate. Accuracy is best when your set was heavy and was 10 reps or fewer. Studies comparing the equations find that different ones fit different lifts and different people best, so expect an error of several percent either way.
Why does this calculator use four formulas and an average?
Each equation was fitted to a different group of lifters and behaves a little differently at different rep counts. Averaging four common formulas gives a steadier number, and the range between the lowest and highest shows how uncertain the estimate is.
Is it safe to test my true one-rep max?
It carries more risk than lighter sets, because form breaks down at maximal loads. If you do it, warm up thoroughly, use a spotter or safety bars, and avoid it when tired. Many coaches prefer estimating a max from a set of 3 to 8 reps instead.
Can I use the same estimate for every exercise?
No. Your one-rep max is specific to each lift, such as the bench press, squat or deadlift, so calculate each one from a set on that exercise. Estimates for small or complex lifts tend to be less reliable.
Why are reps limited to 12?
Beyond about 10 to 12 reps, endurance, pacing and discomfort affect the set as much as strength, so the equations become unreliable. For a better estimate, do a heavier set of fewer reps.
Disclaimer and editorial note
For information only, not medical advice. This calculator gives general estimates from the numbers you enter. It cannot diagnose, treat or prevent any condition and does not replace advice from a doctor, midwife, registered dietitian or other qualified professional who knows your history.
Written and maintained by the HealthFitnessHQ editorial team. We name the source of every formula and category used, and we review each calculator when guidance changes. Read how we work in our editorial policy and methodology.