Free Tool
1RM Calculator
Enter the weight you lifted and the reps you completed. We estimate your one-rep max using the Epley formula, the same calculator built into the Virtus Athlete app.
How the 1RM Calculator Works
A one-rep max (1RM) is the most weight you can lift for a single repetition. Knowing it lets you set training percentages accurately, plan progressions, and compare lifts across exercises. Actually attempting a true 1RM is risky and rarely necessary. The Epley formula estimates your max from any submaximal set.
The Epley Formula
1RM = weight × (1 + reps / 30)
The formula is most accurate in the 2-10 rep range. Below 2 reps it overestimates. Above 10 reps muscular endurance becomes a bigger factor than pure strength, and the estimate loses reliability.
Reverse: Weight for a Target Rep Range
The same formula reverses to give the weight for any rep target: weight = 1RM / (1 + target_reps / 30). That is what powers the working-weights table above.
For the deeper write-up, including the percentage table and when the estimate breaks down, read the full article: 1RM Calculator: Estimate Your One-Rep Max.