One Rep Max Calculator
Adjust the inputs below. Results update as you type.
How it works
Epley formula: 1RM = weight × (1 + reps/30). Brzycki: 1RM = weight / (1.0278 − 0.0278 × reps). Most accurate for 3–10 reps; less reliable above 12 reps. Use 1RM to set training percentages: strength work at 85–95%, hypertrophy at 65–85%, endurance below 65%. Actual 1RM varies with fatigue, technique, and daily readiness—test in controlled conditions.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
The Epley formula estimates one-rep max: 1RM = weight × (1 + reps ÷ 30). The Brzycki formula uses 1RM = weight × 36 ÷ (37 − reps).
Worked example
Lifting 200 lb for 5 reps estimates a 1RM of 200 × (1 + 5/30) = 200 × 1.167 ≈ 233 lb by the Epley formula.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
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Frequently asked questions
What is a one-rep max?+
The most weight you can lift for a single repetition of an exercise. It gauges maximal strength and helps set training percentages.
How accurate is the estimate?+
Estimates are most reliable under about 10 reps. Beyond that, endurance affects the result and the predicted 1RM becomes less precise.
Is testing a true 1RM safe?+
It carries injury risk and needs proper warm-up, form, and a spotter. Rep-based estimates are a safer way to track strength for most people.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.