The One Rep Max calculator estimates the maximum weight you can lift for a single repetition (1RM) based on a lighter weight lifted for multiple reps. This is essential for structuring progressive overload training programs based on percentages of your 1RM.
Enter the weight lifted and number of repetitions completed. The calculator applies the Epley formula (1RM = weight × (1 + reps/30)) and other validated formulas, giving a consensus estimate. Most accurate when using sets of 3–10 reps — very high rep sets (15+) produce less accurate 1RM estimates.
Training programs commonly prescribe intensity as a percentage of 1RM: 85–90%+ for strength, 70–80% for hypertrophy, 50–65% for endurance training.
Reach for this calculator when you need a standardised health metric to discuss with a healthcare provider or to use as a baseline for a fitness programme. The result gives you a number that carries more meaning than subjective assessments.
A frequent error is failing to control measurement conditions between calculations. Weight and body circumferences vary significantly throughout the day and with hydration levels. Always measure under the same conditions (same time of day, same equipment) to make comparisons meaningful.
A nurse calculates a patient's health metric during a routine assessment, then uses the result alongside other clinical indicators to contextualise the finding — correctly treating the number as one data point among several rather than a standalone answer.
Epley 1RM Formula
1RM = Weight × (1 + Reps ÷ 30)
Most widely used formula. Valid for 1–10 rep ranges. For very high rep counts (15+), use Brzycki: 1RM = Weight × 36 ÷ (37 − Reps).
You squat 120kg for 4 reps. What is your estimated 1RM?
Result: Estimated 1RM = 136kg. Train at 80% = 109kg for hypertrophy work.
Use the Epley formula: 1RM = Weight × (1 + Reps/30). For example, benching 100kg for 5 reps: 1RM = 100 × (1 + 5/30) = 116.7kg.
Strength (1–5 reps): 85–100% 1RM. Hypertrophy (6–12 reps): 65–85%. Muscular endurance (12+ reps): under 65%. Use the percentage table to calculate your working weights.
CalcPlanet – Free Online Calculators
725+ free calculators and 108 tools for math, money, health, and everyday life. Instant results, verified formulas, no sign-up.
By CalcPlanet Editorial · Reviewed against our Editorial Standards and Formula Sources.
CalcPlanet calculators are free, privacy-first, and formula-reviewed.
Editorial Standards · Formula Sources · Privacy · Terms · Contact
