One Rep Max Calculator
Estimate your one-rep max from a weight and rep count using the Epley formula.
Your one-rep max (1RM) is the heaviest weight you could lift for a single rep — useful for programming training percentages, but risky and impractical to test directly for most lifts. This estimates it from a lighter set you can safely perform.
The Epley formula
This uses the Epley formula: 1RM = weight × (1 + reps/30). It's one of several established estimation formulas (others include Brzycki and Lombardi) and tends to be reasonably accurate for rep ranges under about 10 — estimates get less reliable at very high rep counts, since fatigue and form start to matter more than pure strength.
Using the percentage table for programming
Most strength programs prescribe training weight as a percentage of your 1RM — for example, "work up to 3 sets of 5 at 80% of 1RM." The percentage breakdown shown alongside your estimate lets you translate program percentages directly into actual weight on the bar.
Frequently asked questions
Is this safe to use instead of testing my real 1RM?
For most training purposes, yes — estimating from a moderate-rep set (say, 3-8 reps) is safer and more practical than attempting a true single-rep max, and it's accurate enough for programming purposes.
Why does my estimated 1RM change between different rep ranges?
Estimation formulas assume a fairly direct fatigue relationship, but very high-rep sets (15+) introduce more variability from muscular endurance and form breakdown, making the estimate less reliable — lower rep sets (3-8) tend to give more consistent estimates.