HEALTH · ONE-REP MAX
One-Rep Max Calculator
Estimate your one-rep max (1RM) from any weight and rep count using six sports-science formulas — Brzycki, Epley, Lombardi, Mayhew, O'Conner, and Wathan — in lb or kg.
Formula accuracy decreases above 10 reps. All estimates are informational — test with caution and always use a spotter.
About This Calculator
Enter any weight and the number of repetitions you completed to estimate the maximum you could lift for a single rep. The calculator computes six established sports-science formulas side-by-side so you can compare them and track your strength progress over time.
How It Works
Each formula uses a weight × reps combination to predict the theoretical maximum for one repetition. Estimates are most accurate in the 3–10 rep range; all formulas become less reliable above 12 reps because fatigue and technique vary more. Switch between lb and kg at any time — the stored value converts automatically.
The Formula
1RM ≈ weight × 36 / (37 − reps) [Brzycki]
- weight
- load lifted in the working set (lb or kg)
- reps
- repetitions completed (1–36)
Frequently Asked Questions
- Which 1RM formula is most accurate?
- No single formula is universally most accurate. Brzycki and Epley are the most widely cited and perform similarly in the 3–10 rep range. Mayhew and Wathan use an exponential model that can be more accurate at higher rep counts. Using the average of all six formulas is a common pragmatic approach.
- How many reps should I use for the most reliable estimate?
- Estimates are most reliable with 3–10 reps. Above 12 reps, fatigue, form breakdown, and psychological factors increase prediction error significantly. For the most accurate estimate, test with a weight you can lift 3–5 times with good form.
- Can I use this to test my actual 1RM?
- These are estimates only. Testing a true 1RM requires proper warm-up, a spotter, and specific protocols. Estimate your range first, then test cautiously in a structured session with a qualified trainer or training partner.