Free Tool
1 Rep Max Calculator
Enter the weight you lifted and how many reps you performed. We'll estimate your one rep max using the Epley formula and show you training percentages for programming your next block.
Hercules tracks your PRs and calculates your 1RM automatically from your logged sets — no manual math.
Download on Google PlayWhat is a one rep max calculator?
A one rep max (1RM) is the maximum weight you can lift for a single repetition with good form. It is the standard measure of absolute strength for any given exercise. A 1RM calculator estimates that number from a set you actually performed — for example, a weight you lifted for five reps — using a mathematical formula. This is useful because performing an all-out max attempt every training session is fatiguing and carries injury risk. Instead, lifters use calculated 1RMs to set training loads, program percentages for strength and hypertrophy work, and track strength progress over time without testing to failure.
Frequently Asked Questions
What is a 1 rep max calculator?
A 1 rep max calculator estimates the maximum weight you could lift for a single repetition based on a lighter weight you performed for multiple reps. It lets you gauge your strength without the risk of an all-out max attempt every session.
How accurate is a 1RM calculator?
Calculated 1RMs are estimates, not guarantees. Accuracy is generally best when using sets of 3–6 reps. Higher rep sets (10+) introduce more variability because individual fatigue resistance and form breakdown differ between athletes.
What formula does this calculator use?
This calculator uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). It is one of the most widely cited 1RM estimation formulas in strength training research and works well across a broad range of exercises and rep ranges.
How often should I test my actual 1RM?
Most coaches recommend testing your true 1RM no more than 2–4 times per year, typically at the end of a training block. For day-to-day programming, calculated estimates from working sets are safer and less taxing on your body.