One-rep max estimator

1RM math — three formulas averaged, because no single one is right

Three classic 1RM estimators, each calibrated against different rep ranges:

• Brzycki (most cited): weight × 36 / (37 - reps) — accurate at 2-10 reps, breaks down outside
• Epley: weight × (1 + reps/30) — slightly conservative, smoother across rep ranges
• Lombardi: weight × reps^0.10 — power curve, holds up better at higher reps

The arithmetic mean of all three is more robust than any single formula. At 3-6 reps the spread is tight (within 2-3%); at 10+ reps the formulas diverge and accuracy drops.

How to use this

• Test set: pick a weight you can move with strict form, RIR 0 (no reps left in tank). Aim for 3-6 reps for best accuracy.
• Use the estimate, not the test: program training off the estimated 1RM, not your tested 1RM. Testing every cycle burns recovery.
• 80% / 70% column: typical strength block uses 70-90% of 1RM. The columns shown are common training percentages.

Caveats

These formulas assume standard barbell movements (squat, bench, deadlift, OHP). They overshoot on high-velocity lifts (cleans, snatches) and undershoot on slow grinders (deadlifts done to lockout from a dead stop).

Track 1RM trends, not absolute values. A 5 lb week-over-week increase in estimated 1RM means progress; the absolute number matters less than the slope.