One Rep Max Calculator
This calculator is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personal health decisions.
1RM estimated from submaximal weight and reps (multiple formulas)
How One Rep Max Is Estimated
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. Testing a true 1RM requires a spotter, warm-up protocol, and carries injury risk — so coaches and lifters often estimate it from a submaximal set. Enter the weight you lifted and how many reps you completed (typically 2–12). The calculator applies six published formulas and averages them for a practical estimate.
The Epley formula is widely used: 1RM = weight × (1 + reps ÷ 30). For 100 kg × 5 reps: 100 × (1 + 5/30) = 116.7 kg. Brzycki uses 1RM = weight × (36 ÷ (37 − reps)); the same example gives 112.5 kg. Lombardi applies a power law: weight × reps^0.10. Mayhew and Wathan use exponential decay models calibrated on larger datasets. O'Conner uses a simple linear factor: weight × (1 + 0.025 × reps).
Because no formula is perfect for every lifter, this tool shows all six results plus an average. It also lists training percentages from 50% to 95% in 5% steps — useful for programming working sets — and rep-range guidance for strength (1–5 reps, 85–100%), hypertrophy (6–12 reps, 67–85%), and endurance (12–20 reps, 50–67%).
Accuracy drops at very high rep counts; these equations assume reps reflect near-maximal effort, not warm-up sets. Technique, fatigue, and exercise selection (squat vs. biceps curl) all affect transferability. Use estimates to plan progressive overload, not as competition attempts without proper preparation.
Examples
| Example | Result |
|---|---|
| 100 kg × 5 reps (Epley) | 116.7 kg estimated 1RM |
| 100 kg × 5 reps (Brzycki) | 112.5 kg estimated 1RM |
| 225 lbs × 3 reps | ~247 lbs average estimate |
| 80 kg × 8 reps | ~100 kg average estimate |
Frequently asked questions
No single formula wins for every lifter. Epley and Brzycki are popular for moderate rep ranges (3–10). Averaging multiple formulas often gives a practical middle estimate.
Most formulas work best between 2 and 10 reps. Above 12 reps, estimates become less reliable because fatigue and endurance dominate.
Hypertrophy is typically programmed at 67–85% of 1RM, corresponding roughly to 6–12 reps per set depending on exercise and rest.