One rep max calculator
Using this one rep max calculator, estimate your one-rep max (1RM) using the weight you lift and the number of repetitions you complete.
One Rep Max Calculator
Result
Estimated max reps
Repetitions
| Repetitions | Weight | % of 1RM |
|---|
| % of 1RM | Weight | Repetitions |
|---|
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What is a one rep max?
A one-repetition maximum (1RM) is the maximum amount of weight you can lift for one complete repetition of a specific exercise while maintaining proper form. It is commonly used to measure muscular strength and determine appropriate training weights.
For example, if you can bench press 80 kg for one repetition, your bench press 1RM is 80 kg. Your maximum will differ across exercises because each movement involves different muscles and lifting techniques.
You do not need to attempt your heaviest possible lift to estimate your 1RM. A one-rep max calculator uses the weight you can lift for multiple repetitions to predict your maximum strength. This allows you to estimate your lifting capacity without performing a potentially demanding maximal attempt.
How is one rep max calculated?
One-rep max formulas use the weight lifted and the number of repetitions completed to estimate the maximum weight you could lift once.
Two commonly used methods are the Epley and Brzycki formulas.
Epley formula:
Brzycki formula:
Lombardi formula:
where:
- Weight is the amount of weight lifted.
- Repetitions is the number of repetitions completed.
- 0.10 is the exponent used in the formula.
For example, if you lift 80 kg for 6 repetitions:
- Epley formula: 80 × (1 + (6 ÷ 30)) = 96 kg
- Brzycki formula: 80 × 36 ÷ (37 − 6) ≈ 92.9 kg
- Lombardi formula: 80 × 6⁰·¹⁰ ≈ 95.7
The formulas produce slightly different estimates because they use different mathematical relationships between repetitions and maximum strength.
Why calculate your one rep max?
Your estimated 1RM can help you:
- Choose training weights: Calculate the loads corresponding to different percentages of your maximum.
- Monitor strength progress: Compare estimates from workouts performed under similar conditions.
- Plan your workouts: Use your estimated maximum as a reference when organizing training intensity.
- Set strength goals: Establish measurable targets for specific exercises.
For example, if your estimated bench press 1RM is 100 kg, lifting 70% of that maximum corresponds to 70 kg.
One rep max percentage chart
The following table shows training weights calculated from an estimated 1RM of 100 kg.
| Percentage of 1RM | Training weight |
|---|---|
| 50% | 50 kg |
| 60% | 60 kg |
| 70% | 70 kg |
| 75% | 75 kg |
| 80% | 80 kg |
| 85% | 85 kg |
| 90% | 90 kg |
| 95% | 95 kg |
| 100% | 100 kg |
These percentages indicate the weight relative to your estimated maximum. They do not guarantee a specific number of repetitions, since performance varies between individuals and exercises.
How accurate is a 1RM calculator?
A one-rep max calculator provides an estimate rather than an exact measurement of your strength. Its accuracy depends on the formula used, the exercise, your training experience, and the number of repetitions performed.
Estimates based on relatively low-repetition sets are often more useful for strength programming than estimates based on long sets, where muscular endurance and fatigue can have a greater influence.
For consistent progress tracking, use the same formula and compare results from similar workouts.
Safety considerations
Testing your actual 1RM involves lifting a very heavy weight, which requires proper preparation and technique.
- Warm up gradually before attempting heavy lifts.
- Use a spotter or appropriate safety equipment when needed.
- Avoid maximal attempts when fatigued.
- Maintain proper form and stop if you experience pain or lose control.
- If you are new to resistance training, focus on developing your technique before attempting maximal lifts.
You do not need to test your actual maximum to use an estimated 1RM for workout planning.
Final thoughts
Your one-rep max is a useful reference for understanding your strength and selecting training weights. This calculator allows you to estimate your maximum from a set you have already completed, without requiring you to attempt a maximal lift.
Use the result as a practical guide rather than an exact prediction, and adjust your training weights according to your actual performance.