Use this free online one rep max calculator to estimate the heaviest weight you could lift for a single repetition, using the Epley formula. Enter the weight you lifted and how many reps you performed to see your estimated one rep max plus a reference table of equivalent weights at other rep counts.
How to Use the One Rep Max Calculator
Enter the Weight Lifted in the weight field.
Enter the Reps Performed (between 1 and 15) in the reps field.
Click "Calculate One Rep Max" to see your estimated one rep max.
Review the "Estimated Weight by Reps" table for equivalent weights at other rep ranges.
Frequently Asked Questions
This calculator uses the Epley formula: One Rep Max = weight lifted × (1 + reps ÷ 30).
Rep-based one rep max formulas like Epley's become less accurate at higher rep counts, so this calculator only accepts between 1 and 15 reps and shows an "Invalid input!" message outside that range.
Using your calculated one rep max, the table reverses the Epley formula to estimate the weight you could lift for other common rep counts (1, 3, 5, 8, and 10 reps).
If the weight or reps field is blank, zero, negative, or reps fall outside the 1-15 range, the calculator shows an error message instead of a one rep max estimate.