One Rep Max Calculator

Your One Rep Max is the maximum weight you can lift for exactly one full rep with correct form. It's the standard measure of absolute strength and is used to calculate training loads as percentages — e.g., "work up to 80% of 1RM for 4 sets of 3." Knowing your 1RM lets you programme strength and hypertrophy work scientifically without guessing.

The Epley formula: 1RM = weight × (1 + reps/30). Example: 100 kg × 5 reps → 1RM = 100 × (1 + 5/30) = 100 × 1.167 = 116.7 kg. The Brzycki formula (1RM = weight × 36 / (37 − reps)) tends to give slightly lower estimates. This calculator shows all major formula results and averages them.

1RM formulas are most accurate for 2–6 rep sets. Accuracy decreases significantly above 10 reps — the formulas overestimate 1RM for high-rep efforts. Typical error: ±5% for 3–6 reps, ±10% for 8–10 reps, ±15–20% for 12+ reps. People with more fast-twitch muscle fibre tend to have lower actual 1RM than formulae predict from high-rep work.

For most gym-goers, estimating 1RM from sub-maximal lifts is safer. True 1RM testing carries a higher injury risk — max loads place peak stress on joints, tendons, and the central nervous system. It requires proper warm-up, a trained spotter, and technique that doesn't break down under maximal load. Reserve true max testing for experienced lifters, competitive powerlifters, or supervised strength assessments.

Standard evidence-based percentages of 1RM: Strength (1–5 reps): 85–100%. Power (3–5 reps with speed): 70–85%. Hypertrophy/muscle growth (6–12 reps): 65–85%. Muscular endurance (12–20+ reps): 50–65%. Active recovery: <50%. This calculator generates the exact target weights for every rep count from your estimated 1RM automatically.