How to use this calculator
Enter the weight you lifted and the number of reps you completed in that set. The calculator will estimate your one rep max using three different formulas and show you the average. For best accuracy, use a recent set where you reached near failure in the 3 to 10 rep range.
The percentage chart below your result shows estimated working weights at various intensities, along with the typical rep ranges for each percentage. Use these numbers to program your training based on your specific goal.
Understanding the formulas
The Epley formula is one of the most widely used 1RM prediction equations. It works by assuming a linear relationship between reps performed and percentage of max. It tends to predict slightly higher values at higher rep counts.
The Brzycki formula is considered more conservative, especially for lower rep ranges. Many powerlifting coaches prefer this formula for programming because it produces slightly more realistic estimates when working with sets of 1 to 6 reps.
The Lombardi formula uses an exponential approach and tends to fall between the other two formulas. By averaging all three, you get a balanced estimate that accounts for the strengths of each method.
Frequently asked questions
What is a one rep max (1RM)?
Your one rep max is the heaviest weight you can lift for a single repetition with proper form. It is the gold standard for measuring maximal strength and is used to calculate training percentages for programming.
How accurate are these formulas?
Most accurate for sets of 1 to 10 reps. Above 10 reps, accuracy decreases because fatigue, technique breakdown, and cardiovascular limitations start influencing the set more than pure strength. Expect results within 5 to 10 percent of your actual max.
Should I actually attempt a true 1RM?
Not necessarily. True 1RM attempts carry injury risk, especially without proper peaking and a spotter. Using a calculator with a recent heavy set of 3 to 5 reps gives you a reliable estimate for programming without the risks of maximal singles.
What rep range should I train in for muscle growth?
For hypertrophy (muscle growth), training at 67 to 85 percent of your 1RM for sets of 6 to 12 reps is most effective. This range provides enough mechanical tension and metabolic stress to stimulate muscle protein synthesis while allowing sufficient volume.
How often should I retest my 1RM?
Every 4 to 6 weeks is a good frequency for intermediate lifters. Simply enter a recent heavy set into this calculator rather than attempting a true max each time. This reduces fatigue and injury risk while still keeping your training percentages accurate.