How it works
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is tiring and carries more injury risk, so most lifters estimate it from a heavier set of 2 to 10 reps.
The Epley (1985) and Brzycki (1993) formulas are the most widely used. They agree closely at around 10 reps and differ a little at lower rep counts, where Epley reads slightly higher. The table turns your estimate into training weights for common intensity levels.
Accuracy depends on taking the set close to failure with consistent technique, and varies by lift and person. Results are estimates, not medical advice.
Formula
Epley: 1RM = w × (1 + reps ÷ 30) · Brzycki: 1RM = w × 36 ÷ (37 − reps)
Questions people ask
How accurate are one-rep max calculators?
For sets of about 3 to 10 reps taken near failure, estimates are usually within 5% of a tested max. Accuracy drops with higher reps, fatigue and lifts that rely heavily on technique.
Which formula should I use, Epley or Brzycki?
Both are well established. Brzycki is often slightly more accurate for low-rep sets; Epley is common in apps. Averaging the two is a reasonable middle ground.
What percentage of 1RM builds strength?
Strength work typically uses about 80–90% of 1RM for 2 to 6 reps. Muscle-building often uses 65–80% for 6 to 12 reps.