What is One Rep Max Calculator?
Your one-rep max is the most weight you can lift once with good form in a given exercise. Testing it directly is risky and fatiguing, so lifters use submaximal sets to estimate it. The formulas below all take a weight and a rep count and project a 1RM, differing in how they model the drop-off as reps rise. Epley, Brzycki and Lombardi are the most used; Mayhew and O'Conner add their own calibrations. Estimates are most reliable in the 3–6 rep range, because at higher rep counts technique, endurance and rep-speed variation distort the relationship. The calculator also returns a percentage chart, so you can read the weight for a target number of reps directly — the practical use for programming training loads.
Common Uses for One Rep Max Calculator
- Estimate a 1RM without a maximal test
- Set training loads from a percentage chart
- Track strength progress from regular working sets
- Compare formulas to see the estimate range
- Plan a peaking block around a known 1RM
Percentage chart as a programming tool
Once you have a 1RM, you can read any training load off the percentage chart: 80% for sets of about 8, 85% for 6, 90% for 4. Programs are usually written in these percentages precisely because they scale to the individual.
Why rep estimates fail at high reps
The relationship between reps and load is not linear. At 20 reps, factors other than maximal strength — local endurance, lactate tolerance and technique drift — dominate, so a 20-rep set says little about a true single. Stay in single digits for estimates.
Track the trend, not the number
Re-estimate from your working sets every few weeks. A rising estimated 1RM at the same rep count is proof of progress, and it costs you nothing in extra fatigue.