One Rep Max Calculator

The calculator uses an average of five validated formulas (Brzycki, Epley, Lander, Lombardi, O'Conner) for better accuracy. It's most reliable with 1-10 reps. With higher rep counts (10+), accuracy decreases as factors like muscular endurance affect results.

Testing a true 1RM carries injury risk and requires experience. For most people, estimating from submaximal lifts (3-5 reps) is safer and sufficiently accurate. Only test actual 1RM if you're an experienced lifter with proper supervision.

Re-test or recalculate every 4-8 weeks, or whenever you complete a training block. As you get stronger, your working weights should increase to maintain the intended training stimulus.

It depends on your goal. Strength: 85-95% for 1-5 reps. Hypertrophy (muscle size): 65-80% for 8-12 reps. Muscular endurance: 50-65% for 15+ reps. Most programs cycle through different percentages.

Each formula was developed from different study populations and exercises. Some work better for certain rep ranges or experience levels. By averaging multiple formulas, we get a more robust estimate that accounts for individual variation.

The formulas were primarily validated on compound lifts (squat, bench, deadlift). They're less accurate for isolation exercises, machine exercises, or movements with significant technique components. Use as a general guide rather than exact prescription.

Once you know your 1RM, you can systematically increase weight. For example, if training at 75%, you'd use that weight until you can do more reps, then recalculate your 1RM and adjust working weights accordingly.