One Rep Max (1RM) Calculator
Enter the weight and the number of clean reps you managed to failure. The one rep max calculator estimates your 1RM – the load for exactly one repetition – with two widely used formulas.
Example: Unit: pounds (lb) · Weight lifted 225 lb · Repetitions 5 reps → Estimated 1RM (Epley): 262.5 lb. Source: doi:10.1080/07303084.1993.10606684, Brzycki M.: Strength Testing – Predicting a One-Rep Max from Reps-to-Fatigue. JOPERD 64(1), 1993, S. 88–90. Updated: .
How it is calculated
How the 1RM is estimated
Your 1RM (one-repetition maximum) is the heaviest load you can lift once with good form. Instead of testing it directly, you can extrapolate it from a heavier set taken to failure:
How to calculate your one rep max
- Choose the unit (kg or lb).
- Enter the weight and the number of clean reps to failure (up to 10).
- Read the estimated 1RM by Epley and Brzycki plus the %1RM table.
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Example: 225 lb for 5 reps. Epley: 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb. Brzycki: 225 × 36 ÷ 32 = 253.1 lb. At 10 reps both formulas give the same result; below that Epley estimates slightly higher, above it Brzycki does.
The %1RM chart
The chart inverts each formula and shows roughly which load fits 1 to 10 reps. By Epley, 5 reps correspond to about 85.7% of 1RM, by Brzycki to 88.9%; 10 reps equal 75% in both. For a single rep the calculator uses the weight itself as the 1RM.
Where the formulas come from
The Brzycki formula was published in 1993 in the Journal of Physical Education, Recreation & Dance. The Epley formula goes back to a poundage chart in Boyd Epley's training manual (1985); it is not a peer-reviewed study, but it is widely cited and has been tested in sports science, for example by LeSuer and colleagues (Journal of Strength and Conditioning Research, 1997) for bench press, squat and deadlift.
Limitations
- Rep count: the more reps, the less accurate the estimate. Above 10 reps the calculator shows a warning.
- Exercise and individual: how many reps you can do at a given %1RM depends on the exercise, training status and muscle fibre type.
- Technique: only count clean reps taken to failure.
The result is an estimate, not a training recommendation. It does not replace medical advice, especially if you have health conditions or pain.
More fitness calculators: the body fat calculator, the BMR calculator for calorie needs and the calories burned calculator.
Frequently asked questions
What does 1RM mean?
1RM stands for one-repetition maximum: the heaviest weight you can lift once in an exercise with proper technique.
Which is more accurate, Epley or Brzycki?
Neither is better across the board. At low reps they are close, and at exactly 10 reps they are identical. Studies find one or the other closer to the measured value depending on the exercise and group tested.
Why only up to 10 reps?
As reps increase, muscular endurance plays a larger role and the formulas drift further from the true 1RM. Sets of up to about 10 reps give the most reliable estimates.
What percentage of 1RM is 8 reps?
By Epley about 100 ÷ (1 + 8 ÷ 30) = 78.9%, by Brzycki (37 − 8) ÷ 36 = 80.6% of 1RM.
Do I need to test my true 1RM?
No. That is exactly why estimation formulas exist: they avoid a maximal attempt. If you have health concerns, check with a doctor before heavy training.
Sources and legal basis
- doi:10.1080/07303084.1993.10606684: Brzycki M.: Strength Testing – Predicting a One-Rep Max from Reps-to-Fatigue. JOPERD 64(1), 1993, S. 88–90
- Epley formula 1RM = weight × (1 + 0.0333 × reps) after Epley B., Poundage Chart, Boyd Epley Workout, 1985 – cited in Frontiers in Sports and Active Living 2025, equations 1 and 2
- Richens B., Cleather D. J.: Biology of Sport 31(2), 2014 – Classification of the 1RM tables (Epley: a table, not a scientific study)
As of: · Editorial policy
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