Deadlift 1RM Calculator

Within about 5 percent at 1 to 5 reps, then accuracy falls off quickly. Validation studies (LeSuer et al., Journal of Strength and Conditioning Research 1997; Wood et al., 2002) report mean absolute errors of 2 to 6 percent across Epley, Brzycki, Lombardi, and O'Conner when reps stay between 1 and 5, with the deadlift sitting on the slightly worse end of the range because grip and lower-back fatigue cut sets short before true muscular failure. Past 8 to 10 reps the formulas lose their grounding in the data they were fit on and the spread between estimates widens to 15 percent or more. If you actually need a reliable 1RM number, work up to a heavy single or double rather than relying on a 12 to 15-rep extrapolation.

Epley (1985) is the default in almost every commercial lifting app (Strong, Hevy, FitNotes, Boostcamp) and most coaching spreadsheets. The reason is practical, not theoretical: it is the simplest of the four (1RM = weight x (1 + reps / 30)), it never blows up at high reps (unlike Brzycki, whose 37 - reps denominator approaches zero), and it sits in the middle of the spread for typical 3 to 8 rep training sets. Wayne Epley first published the equation in a 1985 Boyer Coaching Association article. He never claimed it was the most accurate, just the most usable, which is precisely why it became the standard.

Because the formula has a denominator that approaches zero. Matt Brzycki published 1RM = weight x 36 / (37 - reps) in NSCA Journal (1993) as a fit to powerlifting competition data in the 1 to 10 rep range. The 37 - reps term is fine inside that window but at 15 reps the denominator is 22 (estimate inflates ~1.64x), at 20 reps it is 17 (~2.12x), and at 30 reps it would divide by 7 and produce absurd numbers. Brzycki himself recommended capping the formula at 10 reps. Most calculators (this one included) drop Brzycki from the average above the 10-rep cutoff so a single diverging formula does not skew the blended estimate.

A bodyweight ratio can make lifts at different body sizes easier to compare. This calculator uses sex-specific reference ratios for a broad training tier, but those tiers are not population percentiles or competition standards. Technique, lift variation, equipment, age, injury history, and training experience all change the context. Track the same lift and setup over time rather than treating the tier as a verdict.

Both styles use the 1RM as their organizing percentage but apply it differently. Linear (Starting Strength, StrongLifts, Texas Method) cycles in a single block: weeks 1 to 4 build at 70 to 80 percent for 5x5, weeks 5 to 8 intensify at 80 to 90 percent for 5x3, then test a new 1RM. The conjugate method (Westside Barbell, popularized by Louie Simmons) rotates max-effort days at 90 percent or above on rotating variations (deficit deadlift, rack pull, block pull) so the central nervous system stays primed without grinding the same lift weekly, paired with dynamic-effort days at 50 to 60 percent for speed. Linear suits beginners and lifters under a 2x bodyweight deadlift because they can add weight every week. Conjugate suits intermediates and advanced lifters whose progress has slowed and who need variation to keep adapting.