One-Rep Max Calculator
Estimate the most you can lift for a single rep from a set you've already done, plus a training-percentage table for programming.
How the 1RM estimate works
A one-rep max is the heaviest weight you can move for a single clean repetition, and it's the backbone of most strength programs — sets are usually written as a percentage of it. Testing a true max is taxing and, for beginners, risky, so this calculator estimates it from a submaximal set instead: you enter a weight and the number of reps you completed with it.
To keep the estimate stable, the tool averages two widely used equations, Epley and Brzycki. Each has slightly different behaviour across rep ranges, and blending them reduces the odd outlier either produces on its own. The percentage table underneath then translates your estimated max into practical training loads.
Getting a useful number
Rep-based formulas are most accurate in the 2-to-10-rep range. As reps climb, individual differences in endurance and technique widen the error, which is why this tool limits input to 20 reps. For the closest estimate, use a heavy set you finished with good form and one or two reps still in the tank.
Use the percentages as a guide, not gospel. Strength blocks typically live at 80–95% of 1RM, muscle-building work around 65–80%, and lighter technique or conditioning work below that. Bar speed, sleep, and stress all shift how a given load feels on the day, so adjust as needed. Pair your training with our macro calculator to fuel recovery.
Formulas: Epley (1985) and Brzycki (1993), averaged. Estimates are most reliable at 2–10 reps.
Frequently asked questions
What is a one-rep max (1RM)?
Your one-rep max is the most weight you can lift for a single, full repetition of an exercise. It is the standard reference for programming strength training, since most plans prescribe loads as a percentage of your 1RM.
How is 1RM estimated without a max attempt?
This calculator averages two well-known formulas, Epley and Brzycki, using a submaximal set — the weight you lifted and how many reps you managed. Averaging the two smooths out the quirks of either formula for a more stable estimate.
Why does accuracy drop at high reps?
Rep-based formulas are most accurate at around 2 to 10 reps. Beyond that, fatigue and technique vary too much between people, so the estimate becomes unreliable. This tool caps input at 20 reps for that reason; for a true max, test a heavier set.
How should I use the percentage table?
The table shows common training loads as a share of your estimated 1RM. Strength work often sits at 80–95%, hypertrophy around 65–80%, and technique or endurance work lower. Use it as a starting point and adjust to how the weight actually feels.