One Rep Max Calculator
Weight × reps in — 1RM estimate and your training percentages out.
How this is calculated
Epley: 1RM = w × (1 + reps ⁄ 30) · Brzycki: 1RM = w × 36 ⁄ (37 − reps)
Worked example (the defaults): 100 kg × 5 reps → Epley 116.7 kg, Brzycki 112.5 kg — call it 114.6 kg. The two formulas bracket the truth for most lifters at low reps; the gap between them IS the honest error bar, which is why this page never pretends to a single decimal-point answer.
Safety, briefly and seriously
An estimated max is for programming percentages, not for proving. Testing a true 1RM belongs at the end of a training block, warmed up, with spotters or safety pins — the estimate above tells you where to start the attempts (open around 90–95% of it), not what to slap on the bar cold.
Frequently asked questions
How is one-rep max estimated?
From a weight you lifted for multiple reps, via published formulas: Epley (w × (1 + reps/30)) and Brzycki (w × 36 ÷ (37 − reps)). 100 kg for 5 reps estimates 116.7 kg (Epley) or 112.5 kg (Brzycki) — we show both plus their average, honest about the spread.
Which formula is right?
Neither is "right" — they're fitted curves from different populations. Epley runs higher at moderate reps, Brzycki lower; they agree at 1 rep by definition. The average of the two is a sensible working number; a real tested max under supervision is the only truth.
How many reps make a reliable estimate?
Under 6 reps predicts best. Between 6–12 the estimate degrades; beyond 12 reps it becomes guesswork (endurance takes over from strength) — Brzycki's formula literally breaks past 36 reps. Test with a 3–5 rep set for the most trustworthy number.
What are the training percentages for?
Programs prescribe loads as % of 1RM: ~85–95% for strength (1–5 reps), ~70–80% for hypertrophy (6–12), ~60% for technique and volume. The table computes those from your estimate so a "5×5 at 80%" day needs no phone math at the squat rack.