1RM O'Conner
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The O'Conner 1RM Calculator estimates the maximum weight someone can lift in one repetition (1RM) based on the used weight and number of repetitions. The formula is: 1RM = weight × (1 + 0.025 × number of repetitions). This is useful for trainers and athletes who want to track progress without overexerting their bodies.
For example, if an athlete lifts 80 kg for 8 repetitions, the calculation would be 80 × (1 + 0.025 × 8) = 96 kg. This estimation helps plan progressive training and avoid muscle overload. The method is simple and widely used in weightlifting and physical therapy settings.
While convenient, note that the O'Conner formula may not be accurate for extremely high or low loads. Individual variations, such as technique and fatigue, also affect results. Always consult a professional before attempting lifts estimated as 1RM.
This calculator is ideal for those aiming to improve strength and hypertrophy safely. When using the result, adjust loads gradually and prioritize movement quality. Monitoring progress with tools like this contributes to more consistent and healthy development.
Frequently asked questions
How does the calculator estimate 1RM?
It uses the formula 1RM = weight × (1 + 0.025 × repetitions), where weight and repetitions are provided by the user.
Can I trust this calculation for training?
The formula is an estimate. For safe training, use it as a reference and adjust the load based on technique and body comfort.
What if the repetitions are very high?
The method may underestimate 1RM in long sets. Prefer tests with 1-10 repetitions for better accuracy.
Is the calculation valid for all exercises?
It works best for compound exercises (like squats). For isolation exercises, variation is higher, and accuracy may be lower.
Do I need a professional to use this tool?
Professional guidance is recommended to avoid injuries, especially if testing loads close to your estimated 1RM.