One-Rep Max (1RM)

Your one-rep max (1RM) is the most weight you can lift for a single, full-range repetition of a given exercise. It's the foundation of nearly every periodized strength program: 5/3/1, Westside, Sheiko, Smolov, Texas Method — they all prescribe daily weights as a percentage of 1RM.

Actually testing a true 1RM is taxing on the central nervous system and risky outside a meet setting. Estimating it from a 3–10 rep set is the standard approach used by coaches and powerlifters: lift submaximally, plug the result into a formula, and program the next block off the estimate.

Estimates are most accurate in the 2–8 rep range. Sets above 12 reps drift further from a true 1RM because endurance and lactate tolerance start to matter more than maximal strength — a 20-rep set tells you about your engine, not your peak ceiling.

Epley (1985): 1RM = weight × (1 + reps/30). Tends to slightly over-estimate at high reps. Most popular formula in commercial gym apps.

Brzycki (1993): 1RM = weight × 36 / (37 − reps). Hits a singularity at 37 reps and is most accurate in the 2–10 rep window. Probably the best single formula for trained lifters.

Lombardi (1989): 1RM = weight × reps^0.10. The flattest curve — under-estimates 1RM relative to others at low reps, over-estimates at very high reps.

O'Conner (1989): 1RM = weight × (1 + 0.025 × reps). Conservative, linear, and good for rough planning.

Lander (1985): 1RM = 100 × weight / (101.3 − 2.67123 × reps). A slightly more conservative cousin of Epley.

Averaging all five smooths out individual formula bias and almost always lands within 5% of a true tested max for the 3–8 rep range. That's the recommended default in this calculator.

You bench-press 225 lb for 5 clean reps. Plug into the formulas: Epley = 225 × (1 + 5/30) = 262.5. Brzycki = 225 × 36/(37−5) = 253.1. Lombardi = 225 × 5^0.10 = 261.7. O'Conner = 225 × 1.125 = 253.1. Lander = 22500 / (101.3 − 13.36) = 255.8.

Five-formula average ≈ 257 lb. That's your training 1RM. Program your next block off 70% (180 lb) for hypertrophy, 80% (206 lb) for strength, 90% (231 lb) for peaking singles.

If you only got 3 reps, the average jumps to ~245 — a 12-lb difference from the 5-rep set. Higher reps inflate the estimate; that's why 3–5 reps is the gold standard for accuracy.

Don't grind. The estimate assumes the last rep was a full-ROM, no-grind effort with maybe one in the tank. If reps slow dramatically or form breaks, the input weight is too heavy and the estimate will overshoot.

Don't extrapolate from sets above 10 reps for big lifts — for squats and deadlifts especially, anaerobic endurance dominates past 10 and the 1RM estimate drifts high by 10–20%.

Re-test every 6–12 weeks. Your training 1RM moves with you; an estimate from January is stale by March.

Different lifts have different formula sensitivity. Brzycki is most accurate for upper-body presses; Epley tends to be slightly more accurate for lower-body lifts. The five-formula average covers both.

For meet planning, subtract 5% from your estimate as your conservative opener. Save your estimated max for your second or third attempt.