How the 1RM estimate works
A one rep max calculator predicts your single-rep maximum from a set you can already do for multiple reps. The fewer reps and the closer the set is to failure, the more accurate the prediction. Rather than rely on one equation, this tool averages six established formulas for a steadier result, and shows each one so you can see the spread.
The formulas used
- Epley: weight × (1 + reps ÷ 30)
- Brzycki: weight × 36 ÷ (37 − reps)
- Lombardi: weight × reps0.10
- O'Conner: weight × (1 + reps ÷ 40)
- Lander: 100 × weight ÷ (101.3 − 2.67123 × reps)
- Mayhew: 100 × weight ÷ (52.2 + 41.9 × e−0.055 × reps)
Training with percentages of 1RM
Once you know your 1RM, you can set every working weight as a percentage of it. Heavy strength work lives at 85–95% for 1–6 reps, muscle growth at roughly 67–80% for 6–12 reps, and endurance below 67% for higher reps. The chart above converts your estimated 1RM into a target weight for each band.
A quick example
Squatting 245 lb for 3 reps averages out to roughly a 268 lb one-rep max — the six formulas land between 259 and 279 lb. From there, a 90% training single is about 241 lb, and an 80% hypertrophy weight for sets of around 8 is near 214 lb.
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 with good form. It is the standard benchmark for strength and the reference point for setting training loads — most programs prescribe weights as a percentage of your 1RM.
How is 1RM calculated from reps?
Rep-max formulas estimate your 1RM from a weight you lifted for several reps. For example, the Epley formula is 1RM = weight × (1 + reps ÷ 30), and Brzycki is 1RM = weight × 36 ÷ (37 − reps). This calculator runs six well-known formulas and averages them, which is more reliable than trusting any single one.
How accurate are 1RM estimates?
They are most accurate when the set is taken close to failure in the 2–6 rep range. Accuracy drops as reps climb, because endurance and fatigue start to matter more than pure strength. Above about 10–12 reps the estimate is only a rough guide, so use a heavier, lower-rep set for the best prediction.
Should I actually test my true 1RM?
Maximal singles carry a higher injury risk and require a thorough warm-up, good technique, and ideally a spotter. Estimating your 1RM from a submaximal set is safer and accurate enough for programming, which is why most lifters and coaches prefer it to repeatedly maxing out.
What percentage of my 1RM should I train at?
It depends on the goal: strength work typically uses 85–95% of 1RM for low reps, hypertrophy (muscle growth) sits around 67–80% for moderate reps, and muscular endurance uses 60% or less for higher reps. The percentage chart in this tool shows the estimated weight and rep range for each level.
Does 1RM differ between exercises?
Yes — your 1RM is specific to each lift. A deadlift 1RM is usually higher than a squat, which is higher than a bench press, and the rep-to-max relationship varies a little by movement. Calculate and track a separate 1RM for each exercise you program.
Sources: Estimates average six published one-rep-max equations — Epley (1985), Brzycki (1993), Lombardi (1989), O'Conner et al. (1989), Lander (1985), and Mayhew et al. (1992). Last reviewed June 2026 by the CalcQuill editorial team.
Disclaimer: These are estimates, not guarantees of what you can safely lift. Strength varies with fatigue, technique, sleep, and the exercise. Always warm up, use good form, and consider a spotter before attempting heavy loads. This tool does not provide medical or coaching advice.