TOOLS / ONE REP MAX
One-Rep Max Calculator
Estimate your one-rep max from a recent set using four formulas (Epley, Brzycki, Lombardi, O'Conner), with a %RM conversion table.
Know your limit — safely.
These are research-based estimation formulas, and results vary by individual. They are not a substitute for medical judgment — consult a doctor if you have a medical condition.
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Testing and using this safely
- If you test your 1RM directly, always use a spotter or safety bars.
- If you're new to training, using the estimated value from this tool is recommended over direct testing.
Formula & Sources
From your reps and weight lifted, we calculate your one-rep max (1RM) using the four formulas below, and show their average as your "estimated 1RM."
- Epley: weight × (1 + reps ÷ 30)
- Brzycki: weight × 36 ÷ (37 − reps)
- Lombardi: weight × reps^0.1
- O'Conner: weight × (1 + 0.025 × reps)
When reps = 1, these formulas aren't applied — the weight you entered is used directly as your 1RM, since formulas would introduce error versus the actual measured value.
Accuracy tends to decline at 11 or more reps; these formulas are generally considered valid up to around 10 reps.
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Reviewed by
Tomonobu SomedaHead Trainer at well-being-life Gym
What research shows, and what happens on the gym floor — I check our content against both.
Content reviewed from the perspective of coaching practice and supplement-industry experience
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