Your one-rep max,calculated seven ways.
Most calculators use one formula and call it a day. This one runs all seven, reconciles them into a confidence-banded estimate, then hands you the full percentage chart, the plate math, and where your number ranks. Punch in your best set.
How a one-rep max calculator works
Your one-rep max (1RM) is the most weight you can lift for a single rep of an exercise. You don't have to actually attempt a true max to know it — the relationship between the weight you lift and the reps you get is predictable enough that a heavy set of a few reps can estimate it accurately, and far more safely.
Every estimate comes from a formula, and there are several well-known ones — Brzycki, Epley, Lander, Lombardi, O'Conner, Mayhew, and Wathan. Each is most accurate in a certain rep range. Rather than pick one, this calculator runs all of them, shows you the spread, and reports a consensus with a confidence range — so a 3-rep set (high confidence) reads very differently from a 15-rep set (a ballpark).
Common questions
How accurate is a 1RM calculator?
For sets of 5 reps or fewer, a good 1RM estimate is typically within a few percent of a true tested max. Accuracy drops as reps climb, because the relationship between reps and load stops being linear past about 10 reps. That is why this calculator runs seven formulas, shows the range between them, and flags low-confidence estimates instead of pretending one number is exact.
Which 1RM formula is most accurate?
No single formula wins everywhere. The Brzycki formula is generally the most accurate for low-rep sets (around 10 reps or fewer), while Epley and the research-derived Mayhew and Wathan formulas hold up better at higher reps. This tool uses Brzycki as the headline number at 10 reps and under, and a consensus average of all valid formulas above that.
How many reps should I use to estimate my one-rep max?
Use a heavy set of 2 to 5 reps taken close to failure. That range gives the most accurate estimate while staying far safer than attempting a true max. Sets above 10 reps can still be used, but expect the estimate to be a wider ballpark.
What percentage of my 1RM should I train at?
It depends on the goal: roughly 85 to 100 percent for maximal strength (1 to 5 reps), 67 to 85 percent for hypertrophy (6 to 12 reps), and below 67 percent for muscular endurance. The percentage table this tool generates gives you the exact loads for your number so you can program sets directly off it.
Can testosterone or hormone levels affect my strength?
Testosterone is a primary driver of muscle protein synthesis, recovery, and the ability to build strength over time. When training is dialed in but progress has stalled for months, low testosterone is one of several factors a clinician can check with bloodwork. This tool is educational and does not diagnose anything; a plateau is worth a conversation with a provider, not a self-diagnosis.