One-rep max (1RM) calculator

Why 1RM matters in strength training

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It's the foundational number in strength sports — used for powerlifting and weightlifting classifications, strength standards by body weight, and — most practically — percentage-based programming. Every major strength program (5/3/1, Texas Method, Conjugate, Bulgarian Method) uses 1RM percentages to prescribe training loads.

Why you should rarely attempt a true 1RM

A maximal single-effort lift carries real risk: form breakdown under extreme load, CNS fatigue that can impair training for 3–5 days, and injury probability that rises sharply at true max effort. Most trainees and coaches estimate 1RM from a well-executed set of 3–5 reps — close enough to use for programming, far from the injury zone. True 1RM attempts are reserved for competition or peaking phases, not regular training.

The five formulas — and why they diverge

Each formula makes different assumptions about the rate at which fatigue accumulates per rep:

• Epley (1985) — the most widely used. Uses a linear factor (r/30). Slightly overestimates at low rep ranges; performs well at 6–10 reps.
• Brzycki (1993) — uses a diminishing denominator (36 / (37 − r)). More conservative at high reps; excellent at 5–8 reps. Comes from research on football athletes.
• Lander (1985) — a percentage-based equation derived from a regression across multiple sports. Performs consistently across the 1–10 rep range.
• Lombardi (1989) — uses a power function (r^0.10). More aggressive than Epley; can overestimate significantly at higher reps.
• O'Conner et al. (1989) — a simple linear formula. Tends to underestimate slightly but is very stable.

Formulas diverge most at high rep counts. At 3 reps, all five are within 2–3% of each other. At 10 reps, the spread can reach 10–15 lbs. This is why averaging all five produces a more robust estimate than relying on any single formula.

The rep limit: why 10+ reps become unreliable

Above 10 reps, neural and cardiovascular factors start dominating what was previously a pure strength test. Your failure point at 12 reps is partly limited by lactate clearance, breathing pattern, and pain tolerance — not just how much force your muscles can produce. The classic 1RM estimation formulas assume that fatigue per rep is consistent, which holds well from 1–10 but not beyond. If you can do 15 reps with a weight, you can still estimate a 1RM — but the confidence interval widens significantly.

How to use training percentages

The training percentage table shows what weight corresponds to each intensity zone. Some common programming benchmarks:

• 50–60% — warm-up and speed work; submaximal effort with fast bar speed
• 70–75% — hypertrophy range; 8–12 reps with moderate load
• 80% — strength-hypertrophy; 4–6 reps, high-effort sets
• 85% — strength work; 3 reps, top sets
• 90–93% — near-max singles; 1–2 reps
• 95% — competition attempts or peaking; reserve for prepared lifters

Use 90–95% of your estimated 1RM as your "training max" — the number you base your percentages on. This built-in buffer accounts for daily variation, the estimation error in the formula, and the difference between a calculated 1RM and what you'd hit on a competition-ready peak day.