One Rep Max (1RM) Calculator
Estimate a single-repetition maximum with the Epley equation. This is an estimate, not a recommendation to attempt a maximal lift.
What is One Rep Max?
Short answer: One Rep Max, or 1RM, estimates the greatest load lifted once with correct technique. This tool uses Epley: 1RM = weight × (1 + repetitions ÷ 30). For one repetition, it uses the entered weight directly.
Frequently asked questions
How accurate is the 1RM estimate?
It is an estimate that varies with exercise, experience, fatigue and technique. Lower repetition counts generally produce more reliable estimates.
Do you need to attempt an actual 1RM?
No. Estimates can support training planning without requiring an actual maximum-load test.
How can the result inform training?
Use it only as a reference. Begin with a load you can control and adjust to experience, goals and advice from a qualified trainer.
Content reviewed: 24 August 2026 • Prepared by the MuscleStationTH team
One Rep Max: limitations and sources
Equation results are estimates, not guaranteed maximum strength. Error depends on exercise, experience, technique, range of motion, fatigue and repetition count. Research generally finds better predictions from lower-repetition sets.
Caution: Do not immediately attempt the estimated maximum load. Beginners and people with injuries, heart conditions, blood-pressure concerns or other health limitations should consult a doctor and qualified trainer.
Further training information
References
- Reynolds et al.: predicting 1RM from multiple-repetition tests (PubMed)
- Accuracy of 1RM prediction equations for bench press and leg extension (PubMed)
- ACSM: resistance training adapted to goals and safety
Content reviewed: 24 August 2026 · Prepared by the MuscleStationTH team