1RM (One Rep Max) Calculator
Estimates 1RM using Epley, Brzycki, Lander and Lombardi formulas with a median comparison across them.
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Understanding 1RM (One-Repetition Maximum)
Your one-repetition maximum (1RM) is the heaviest load you can lift one time with proper form. Testing a true 1RM is risky for untrained lifters, so coaches usually estimate it from submaximal sets with regression equations. The two you'll see quoted most often are Epley, 1RM = w × (1 + r/30), and Brzycki, 1RM = w × 36/(37 - r). Here w is the load you lifted and r is the number of clean reps you got to concentric failure.
Both equations hold up well for sets of 2 to 10 reps. Once you push past about 10, neuromuscular fatigue and the aerobic contribution start to skew the prediction, and the estimate drifts. Averaging a couple of formulas smooths out the bias in any single one and leaves you with a sturdier working number.
Applications
The ACSM and NSCA write strength loads as a percentage of 1RM. Roughly 85% covers 5RM strength and hypertrophy work, 75-80% lands you in 8RM hypertrophy territory, and 90% or more is where max-strength singles and doubles live. Having a 1RM estimate is what lets you add weight safely, lay out training cycles, and stack athletes against each other on relative strength, all without a maximal attempt every single week.
FAQ
Is the estimate accurate above 10 reps? Not really. Validity falls off fast once the endurance and lactic systems take the wheel. Stick to 3-8 reps if you want the tightest estimate.
Epley or Brzycki — which is better? At high reps Brzycki leans a touch low while Epley runs high, so in practice averaging the two is a sensible compromise.
Do I need to test 1RM directly? Most lifters never do. A heavy set of 3-5 reps gives you an estimate that's safer to chase and tells you almost everything you need for programming.
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Max Acceleration (Parabolic Cam)
Calculate the (constant) maximum acceleration of a parabolic-motion (constant-acceleration) cam follower, a_max = (4·h·ω²) ÷ β², from the total lift h (mm), the cam angular velocity ω (rad/s) and the rise angle β (rad). Parabolic, or constant-acceleration, motion is the law producing the LOWEST possible maximum acceleration for a given lift and time — so it minimizes peak inertia forces. It consists of two halves: in the first, the follower accelerates with CONSTANT acceleration (rising parabolic displacement); in the second, it decelerates with the same constant (negative) acceleration, stopping at the top. The name 'parabolic' comes from the displacement diagram, formed by two parabolas. The great advantage is the low maximum acceleration; the drawback is that acceleration JUMPS abruptly — from +a_max to −a_max at the middle, and from zero to ±a_max at the ends — generating infinite JERK there, causing shocks, noise and vibration. So in practice pure parabolic is little used at high speed (despite low peak acceleration), and cycloidal or modified profiles that smooth these transitions are preferred. Parabolic is didactic and useful when peak acceleration is the limiting factor and speeds are moderate. Enter the lift, the angular velocity and the rise angle.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.