The formula
Epley formula: 1RM = weight × (1 + reps ÷ 30). It's the most widely used estimate and holds up well up to ~10 reps; beyond that, estimates drift and real 1RM attempts (with a spotter) are safer. Lighter variations include Brzycki (1RM = w × 36 / (37 − reps)).
Training zones (% of 1RM)
- 1–5 reps, 85–100% — strength / neural adaptation
- 6–12 reps, 67–85% — hypertrophy (muscle growth)
- 12–20 reps, 55–67% — muscular endurance
- Power work — 40–60% moved fast
Rest enough between sets (2–5 min for strength, 60–90 s for hypertrophy), and re-test every 4–6 weeks as you progress. The estimate is a planning tool; form and safety beat any number.