One Rep Max Calculator
Estimate your maximum one-rep lift weight from submaximal sets
Estimated 1 Rep Max
How to Use
- Enter the weight you lifted in your set.
- Enter the number of repetitions you completed (1–15).
- Select the weight unit (kg or lbs).
- Click 'Calculate 1RM' to see estimates from four different formulas.
- Use the training table to find appropriate weights for different rep ranges.
About One Rep Max
What is 1RM?
The one-repetition maximum (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength. While directly testing 1RM is effective, it carries injury risk, especially for beginners. Submaximal estimation formulas provide a safer alternative.
The Four Formulas
Brzycki: weight × 36/(37 − reps) — most accurate for 1–10 reps. Epley: weight × (1 + 0.0333 × reps) — widely used in fitness software. Lombardi: weight × reps^0.1 — tends to give slightly higher estimates. O'Conner: weight × (1 + 0.025 × reps) — more conservative estimate. Accuracy decreases above 10 reps for all formulas.
Training Percentages
50% 1RM: 20+ reps, light warm-up sets. 60% 1RM: 15–20 reps, endurance training. 70% 1RM: 10–15 reps, hypertrophy focus. 80% 1RM: 6–10 reps, strength and size. 90% 1RM: 3–5 reps, strength training. 95%+ 1RM: 1–3 reps, max strength/powerlifting.
Accuracy and Safety
For best accuracy, use a weight you can lift for 3–8 reps (closer to failure). Avoid using sets where you complete more than 12 reps, as formula accuracy significantly decreases. Never attempt a true 1RM without a spotter and proper warm-up. Rest 3–5 minutes between near-maximal sets to ensure full recovery.
Key Features
- Uses four different validated formulas for comparison
- Shows training percentage table for programming
- Supports both kg and lbs
- Safe way to estimate max strength without testing to failure