One Rep Max
Calculator
Estimate your absolute maximum strength for any lift. Use clinical formulas to find your theoretical peak performance and calculate training percentages for your next block.
Safety First: Testing a true 1RM is physically taxing and increases injury risk. Our calculator uses submaximal data (weights you can lift for 2-10 reps) to predict your 1RM with high accuracy.
Mastering Your Max
Your One Rep Max (1RM) is the heaviest weight you can lift for a single, full-range-of-motion repetition. It is the gold standard for measuring raw strength.
In the world of strength training, 1RM isn’t just a number to brag about—it’s a tool for program design. Most effective strength programs (like 5/3/1 or the Juggernaut Method) don’t tell you to lift “heavy weight.” They tell you to lift a specific percentage of your 1RM.
Epley vs. Brzycki: Which is Better?
While there are dozens of formulas, the two most clinically recognized are:
- The Epley Formula: Created in 1985 by Boyd Epley, the founder of the NSCA. It is the most popular formula because it tends to be more accurate for “rep-heavy” sets. It uses the calculation:
Weight × (1 + 0.0333 × Reps). - The Brzycki Formula: Created by Matt Brzycki in 1993. This formula is often considered slightly more conservative and is arguably more accurate for lower rep ranges (sets of 2-5 reps). It uses the calculation:
Weight / (1.0278 - (0.0278 × Reps)).
The Accuracy Limit
These formulas are statistically accurate only when the repetitions performed are **below 10 to 12**. If you can lift a weight for 20 reps, it becomes an endurance test rather than a strength test, and these formulas will vastly overpredict your actual 1RM. For the most reliable estimate, use data from a heavy set of 3 to 6 reps.
Strength FAQs
Common questions about testing your max.
Unless you are a competitive powerlifter or weightlifter, there is rarely a biological need to test a true 1RM. Estimated 1RMs are sufficient for 99% of training goals and keep you out of the “danger zone” where form breakdown usually occurs under maximal load.
Handling a true 1RM requires specific neurological adaptations and “skill.” If you train mostly with higher reps, your body might have the raw tissue strength, but your nervous system isn’t primed to stabilize and coordinate a single maximal effort. This is known as “strength specificity.”