1 Rep Max Calculator

Estimated 1RMs are typically accurate to within 5–10% when calculated from 3–10 reps. Accuracy decreases as rep count increases — at 15+ reps, neural fatigue and conditioning play a bigger role than pure strength, making predictions less reliable. For the most accurate estimate, test with a weight you can lift 3–6 times.

It depends on your goal. For maximum strength, train at 85–95% (1–6 reps). For hypertrophy (muscle growth), 67–85% (6–12 reps) is optimal. For muscular endurance, 50–67% (12–20 reps). Most programs cycle through these ranges across different phases of training.

Testing a true 1RM can be done safely with proper preparation, but carries more injury risk than sub-maximal testing. Warm up thoroughly with progressive sets, use a spotter, and never test a true 1RM when fatigued. For most recreational lifters, estimating from a 3–5RM is safer and nearly as useful for programming.