{
  "slug": "one-rep-max-comparison",
  "title": "Multi-Formula 1RM Comparison Calculator",
  "category": "Strength Training",
  "category_slug": "strength-training",
  "tier": 1,
  "summary": "Compare Epley, Brzycki, and Lombardi 1RM predictions side-by-side from a single lift.",
  "description": "This calculator estimates one-rep max (1RM) strength by applying three widely used prediction formulas—Epley (1985), Brzycki (1993), and Lombardi (1989)—to a single submaximal lift and displays each result alongside their average. It requires the weight lifted and the number of repetitions completed, then outputs four 1RM estimates in kilograms. These formulas were derived from regression analyses of submaximal-load data and may vary in accuracy depending on rep range, training status, and exercise selection.",
  "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-comparison/",
  "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-comparison.json",
  "formula": {
    "id": "one_rep_max_comparison",
    "expression": "\\text{1RM} \\in \\{\\text{Epley}, \\text{Brzycki}, \\text{Lombardi}\\}(w, r)",
    "variables": [
      {
        "symbol": "w",
        "description": "Weight in kg"
      },
      {
        "symbol": "r",
        "description": "Reps performed"
      }
    ]
  },
  "inputs": [
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 20,
      "max": 300,
      "step": 0.1
    },
    {
      "id": "reps",
      "label": "Reps",
      "type": "number",
      "unit": "reps",
      "default": 5,
      "min": 1,
      "max": 20,
      "step": 1
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 75,
      "reps": 5
    },
    "expected_output": "86.7 kg"
  },
  "result_summary_template": "With a weight lifted of {weight_kg} kg for {reps} repetitions, the average 1RM across Epley, Brzycki, and Lombardi formulas is estimated at {result}.",
  "methodology": "Applies the Epley formula (1 + reps/30), Brzycki formula (1 / (1.0278 − 0.0278×reps)), and Lombardi formula (reps^0.10) to the lifted weight, then averages the three results. Epley (1985), Brzycki (1993), and Lombardi (1989) each derived regression models from submaximal-load data.",
  "sources": [
    {
      "label": "Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: University of Nebraska Press; 1985.",
      "url": ""
    },
    {
      "label": "Brzycki M. Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88–90.",
      "url": "https://doi.org/10.1080/07303084.1993.10606684"
    },
    {
      "label": "Lombardi VP. Beginning Weight Training: The Safe and Effective Way. Dubuque, IA: Wm. C. Brown Publishers; 1989.",
      "url": ""
    }
  ],
  "faqs": [
    {
      "question": "Why does this calculator show three different 1RM values?",
      "answer": "Each equation—Epley, Brzycki, and Lombardi—uses a different regression model derived from distinct datasets and rep ranges. Small differences in the constants and exponents produce slightly different predictions for the same lift, so displaying all three reveals the range of published estimates rather than relying on a single formula."
    },
    {
      "question": "Which formula is most accurate?",
      "answer": "No single formula is universally most accurate across all lifts, rep ranges, and populations. Research comparing these equations typically finds similar accuracy in the 1–10 rep range, with individual variability exceeding differences between formulas. The average provided here is a simple way to synthesize all three."
    },
    {
      "question": "Can I use this calculator for reps above 10?",
      "answer": "The tool accepts up to 20 repetitions, but prediction accuracy declines as reps increase beyond 10. Higher-rep sets are influenced more by muscular endurance and metabolic factors than by maximal strength, making regression-based 1RM estimates less reliable at those rep counts."
    },
    {
      "question": "Does the average of three formulas improve accuracy?",
      "answer": "Averaging three estimates may reduce the impact of any single formula's bias, but there is no peer-reviewed evidence demonstrating that the arithmetic mean of Epley, Brzycki, and Lombardi is more accurate than each formula individually. It is a convenience calculation, not a validated superior method."
    },
    {
      "question": "What exercises work best with these formulas?",
      "answer": "The Epley, Brzycki, and Lombardi equations were developed and validated primarily using compound barbell lifts—squat, bench press, deadlift, and overhead press. Predictions may be less accurate for isolation exercises, machines, or movements with significant technical variability."
    }
  ],
  "related_tools": [
    {
      "slug": "one-rep-max-brzycki",
      "title": "One-Rep Max Calculator (Brzycki Formula)",
      "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-brzycki.json",
      "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-brzycki/"
    },
    {
      "slug": "one-rep-max-epley",
      "title": "One-Rep Max Calculator (Epley Formula)",
      "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-epley.json",
      "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-epley/"
    },
    {
      "slug": "one-rep-max-lombardi",
      "title": "One-Rep Max Calculator (Lombardi Formula)",
      "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-lombardi.json",
      "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-lombardi/"
    }
  ],
  "last_updated": "2026-04-22",
  "price": {
    "value": 0,
    "currency": "USD"
  },
  "runs_in_browser": true,
  "disclaimer": "Educational estimate produced from a published formula. Not medical, nutritional, or training advice. Calculations are deterministic — apply the formula to the inputs to reproduce the result."
}