What is a one-rep max (1RM)?
Your 1RM is the heaviest weight you can lift for exactly one repetition with proper form. It is the standard benchmark for strength and the anchor for percentage-based training programs — "squat 5×5 at 80%" means 80% of your 1RM. Estimating it from a submaximal set is safer than testing it directly.
How accurate are 1RM formulas?
Quite accurate in the 2–10 rep range — typically within 2–5% for trained lifters. Accuracy drops as reps climb, which is why this calculator caps input at 15. The four formulas (Epley, Brzycki, Lombardi, O'Conner) diverge slightly by rep range, so the average of all four is a robust estimate.
How do I use the training percentage table?
Strength programs prescribe loads as percentages of 1RM: roughly 85–95% for strength work (2–6 reps), 70–85% for hypertrophy (6–12 reps), and 60–70% for endurance and technique work. The table converts your estimated max into actual barbell weights for each zone.
Is it safe to test my true 1RM?
Testing a true max puts high stress on joints and connective tissue and should only be done well-warmed-up, with a spotter or safety pins, and ideally with significant training experience. For most lifters, estimating from a hard set of 3–5 reps gives the programming benefits without the risk — that is exactly what this calculator is for.
Why does my estimated max differ between exercises?
Because rep-max formulas were fitted to particular lifts and do not transfer cleanly. Exercises using large muscle groups over a long range, such as the deadlift, tend to produce fewer reps at a given percentage than the bench press, so a formula calibrated on one will overestimate the other. Technique-heavy Olympic lifts fit worst of all, since form degrades with fatigue before the muscles do. Treat an estimate as reasonable for the lift it was derived from and approximate everywhere else.
Does my one-rep max change from day to day?
Considerably. Sleep, food, hydration, stress, time of day and how recently you trained the same muscles can move true maximal strength by several percent in either direction, and more after a poor week. This is why programmes built on percentages of a max recorded months ago drift out of calibration — the percentages become too easy or, more often, too hard. Autoregulated approaches that set load by how a warm-up feels on the day exist precisely to work around this.