Anton YefanovWhat is a one rep max?
Your one rep max (1RM) is the greatest load you can lift once through the full range of motion of a particular exercise. An estimated 1RM uses a set of multiple reps to approximate that number. It gives you a reference for percentage-based programs and a way to compare similar sessions over time.
Choose a set that tells you something.
Use a recent, hard set of an exercise you know well. Enter only completed reps with consistent technique. For a barbell exercise, count the bar and every plate. For dumbbells, use a consistent convention, such as the weight of one dumbbell; your result will follow the same convention. Keep the exercise, equipment, and range of motion consistent when comparing estimates.
How accurate is a 1RM calculator?
There is no universal error margin. In a study of 103 young women, bench press prediction equations performed better when sets involved fewer than 10 reps. That supports using a lower-rep set, but does not guarantee the same accuracy for every lifter or exercise.
A meta-regression covering 269 studies found that the reps possible at a given percentage of 1RM varied between individuals and exercises. A leg press and a bench press, for example, do not share an identical reps-to-load relationship. Treat your estimate as a reference that you refine with experience.
Three formulas. Three perspectives.
Epley is the default here; you can select Brzycki or Lombardi to see another estimate. Each equation describes the relationship between weight and reps differently. Choosing a formula consistently can make comparisons easier. The spread shows disagreement between equations; your actual max may fall outside it.
| Formula | 1RM equation |
|---|---|
| Epley | weight × (1 + reps ÷ 30) |
| Brzycki | weight × 36 ÷ (37 − reps) |
| Lombardi | weight × reps⁰·¹ |
Here, reps means completed reps plus any reps in reserve you enter. For a single with no reserve, all results equal the entered weight.
How to calculate your one rep max by hand
The Epley formula needs nothing more than a phone calculator.
Take a recent hard set and note the weight and the reps you completed.
Divide the reps by 30, then add 1.
Multiply the weight by that number. The result is your estimated 1RM.
For a training weight, multiply the estimate by the percentage your program asks for.
Other 1RM formulas you will see
Other calculators and spreadsheets often use one of these. They are listed for reference so you can recognise them; this calculator sticks to the three above.
| Formula | 1RM equation |
|---|---|
| Mayhew | 100 × weight ÷ (52.2 + 41.9 × e^(−0.055 × reps)) |
| Wathan | 100 × weight ÷ (48.8 + 53.8 × e^(−0.075 × reps)) |
| O'Conner | weight × (1 + 0.025 × reps) |
| Lander | 100 × weight ÷ (101.3 − 2.67123 × reps) |
Put percentages in context.
To find a prescribed load, multiply your estimated max by the percentage in your program. The table above does that for you. It does not prescribe sets, reps, or a training goal: the same percentage can feel different across exercises and people. Round to an available weight and adjust based on technique, fatigue, and how many reps you can complete.
Bench press, squat and deadlift
Each of the big three has its own calculator page, with notes on which set to enter and how the common variations of the lift compare.
Stopped short of failure?
If you rate your sets by effort instead of counting reps in reserve, the RPE calculator takes the rating directly and gives you a chart of training weights for every rep and effort target.
Frequently asked questions
Can I use this for a bench press, squat, or deadlift?
Yes, you can calculate an estimate for each lift. Use a separate set for each exercise and compare results for the same lift and technique. These general equations do not account for exercise-specific differences, so they should not be treated as equally accurate for every movement.
Which one rep max formula should I choose?
Epley is the default in this calculator. Brzycki and Lombardi offer useful comparisons, but no formula is best for every person and exercise. Keep the same formula when tracking your progress, and compare it with your actual lifting performance.
What if I stopped before I reached failure?
Open “Had a few reps left?” and enter your reps in reserve. The calculator adds those to your completed reps before applying each formula. This is a practical approximation: judging unused reps is subjective and can make the estimate less reliable.
Does switching from kg to lb change the estimate?
The calculator converts the weight you entered, so the underlying load stays the same. Small differences in the displayed numbers come from rounding. One pound is exactly 0.45359237 kilograms.
What do 3RM and 5RM mean?
A 3RM is the most you can lift for three reps, and a 5RM the most for five. The rep max chart above predicts each one from your estimated 1RM, using whichever formula you picked. Like the 1RM itself, these are estimates to check against how your sets actually go.
Do I need to test my actual one rep max?
You can use an estimate to follow percentage-based training without performing a maximal single. A true 1RM test is a different task and requires appropriate preparation, technique, and equipment. This calculator is not a recommendation to attempt the predicted weight.
Sources
Peer-reviewed research on prediction accuracy and the relationship between reps and load. These studies inform the guidance above; they do not validate this calculator or its reps-in-reserve adjustment.
- Accuracy of prediction equations for determining one repetition maximum bench press in women before and after resistance training
Mayhew JL, Johnson BD, LaMonte MJ, Lauber D, Kemmler W. Journal of Strength and Conditioning Research. 2008;22(5):1570–1577.
Compares prediction equations and examines the influence of rep count and training.
- Maximal Number of Repetitions at Percentages of the One Repetition Maximum: A Meta-Regression and Moderator Analysis of Sex, Age, Training Status, and Exercise
Nuzzo JL, Pinto MD, Nosaka K, Steele J. Sports Medicine. 2024;54:303–321.
Examines variation in the relationship between reps and percentage of 1RM.