1 Rep Max Calculator
Estimate your one-repetition maximum and training percentages from any set
1 Rep Max Calculator
Estimate your one-repetition maximum and training percentages from any set
What is a 1 Rep Max (1RM)?
One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with correct technique. It is the foundational metric of strength training — used to prescribe training loads, track progress, and compare strength relative to bodyweight. Most people never actually test their true 1RM (it requires maximum effort and a spotter), so submaximal estimation formulas were developed to predict it from lighter sets.
This calculator uses four validated formulas: the Epley formula (1985) — the most widely used in powerlifting and the default displayed — along with Brzycki, Lombardi, and O'Conner. Each formula was derived from different population studies and tends to agree well for sets of 1–6 reps. Accuracy decreases progressively above 10 reps — for sets of 15+ reps, the estimated 1RM can deviate significantly from reality.
The training percentage table — which maps percentages of 1RM to representative rep ranges — is based on NSCA (National Strength and Conditioning Association) and Prilepin's Chart guidelines. Strength phases typically use 85–95%, hypertrophy 67–85%, and muscular endurance below 65%. These percentages are the backbone of periodised programming used in all professional strength sports.
How to Use This Calculator
Strength Standards — Squat (kg, male, bodyweight ~80kg)
- • Beginner: < 60 kg — just starting structured training
- • Novice: 60–100 kg — several months of consistent training
- • Intermediate: 100–140 kg — 1–2 years progressive overload
- • Advanced: 140–180 kg — multi-year serious training
- • Elite: 180 kg+ — competitive powerlifting level
Why 1RM Estimates Matter for Programming, Not Just Bragging Rights
Testing a true 1RM carries real injury risk, especially for beginners and younger lifters whose technique tends to break down under maximal load and who lack the years of neuromuscular experience to know when a lift is about to fail dangerously. This is exactly why submaximal estimation from a lighter, well-controlled set is the standard recommendation for anyone without a spotter and years of maximal-lift experience, rather than testing an actual 1RM.
Strength coaches use 1RM percentages differently depending on the athlete: a powerlifter's programming is built entirely around progressively approaching a competition-day 1RM, while a cricket or football strength coach uses percentage-based training mainly to manage fatigue during a season — keeping athletes strong without accumulating the kind of heavy-load fatigue that would hurt sport performance on match day.
Formula divergence increases with rep count for a real physiological reason: a 3-rep set is almost purely a test of maximal strength, while a 15-rep set brings in muscular endurance and fatigue resistance as separate qualities. Since the formulas were built assuming a fairly direct relationship between reps and strength, that relationship breaks down at higher reps where a different physiological system is being tested.
?Frequently Asked Questions
Research shows Epley and Brzycki formulas predict 1RM within ±5–10% for most people when the input set uses 2–6 reps at high effort. Accuracy degrades for reps above 10 because the neuromuscular demands of low-rep maximal strength and high-rep muscular endurance diverge. A 2012 meta-analysis in the Journal of Human Kinetics found submaximal prediction equations are valid for practical use when reps are 10 or fewer.