How the one-rep max is estimated
Each formula converts the weight and the number of reps you managed into a predicted single-rep maximum. They were derived from groups of lifters who did both a rep test and a true max, so they describe averages, not you specifically.
Use it for programming
Most strength programs prescribe work as a percentage of 1RM. An estimated max lets you set training loads without testing your max all the time. Many coaches deliberately program from a slightly conservative “training max” (for example 90% of the estimate) to leave room for progress.
Why the formulas disagree at high reps
At 1–5 reps all seven formulas land within a few percent of each other. At 12+ reps the spread widens, because endurance varies so much between individuals and exercises. For the most reliable estimate, use a heavy set of 3–8 reps.
Frequently asked questions
How accurate is a 1RM calculator?
Rep-based estimates are usually closest when the set is between about 2 and 10 reps taken close to failure. Above roughly 10–12 reps the formulas diverge and errors grow, because muscular endurance differs a lot between people and lifts.
Which 1RM formula is best?
No single equation wins for every lift or lifter. Epley and Brzycki are the most widely used, and they agree closely at low reps. Averaging several formulas, as this calculator does, smooths out the bias of any one of them.
Should I test my true one-rep max?
Not necessarily. Many lifters program from estimated maxes or from rating of perceived exertion (RPE) instead of frequent true max attempts, which carry more fatigue and injury risk. If you do test, use a spotter or safety arms and a structured warm-up.
What percentage of 1RM should I train at?
As a general guide from the strength-training literature: roughly 80–100% for maximal strength (1–5 reps), 60–80% for hypertrophy work (6–15 reps), and lighter loads for technique and endurance. Muscle growth has been shown across a wide range of loads, as long as sets are taken close to failure.
What is a good strength-to-bodyweight ratio?
It depends heavily on sex, training age, body size and the lift. Ratios are good for tracking your own progress over time and poor for comparing yourself with people of very different body sizes.
Sources & further reading
- Brzycki M (1993). Strength testing — predicting a one-rep max from reps-to-fatigue . J Phys Educ Recreat Dance 64(1):88–90 · doi:10.1080/07303084.1993.10606684
- LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift . J Strength Cond Res 11(4):211–213
- Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW (2017). Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis . J Strength Cond Res 31(12):3508–3523 · doi:10.1519/JSC.0000000000002200