{
  "slug": "one-rep-max-epley",
  "title": "One-Rep Max Calculator (Epley Formula)",
  "category": "Strength Training",
  "category_slug": "strength-training",
  "tier": 1,
  "summary": "Estimate your one-rep max from submaximal lifts using the classic Epley formula.",
  "description": "This calculator estimates your one-repetition maximum (1RM) using the Epley formula, a widely used linear model published in 1985. It requires the weight lifted and the number of repetitions completed in a single set, then applies the equation 1RM = weight × (1 + reps ÷ 30) to estimate the maximum weight that can be lifted for one rep. The Epley formula is most accurate for rep ranges between 1 and 10, with reliability decreasing as repetition counts approach the validated upper limit.",
  "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-epley/",
  "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-epley.json",
  "formula": {
    "id": "one_rep_max_epley",
    "expression": "\\text{1RM} = w \\times \\left(1 + \\frac{r}{30}\\right)",
    "variables": [
      {
        "symbol": "w",
        "description": "Weight lifted in kg"
      },
      {
        "symbol": "r",
        "description": "Reps performed"
      }
    ]
  },
  "inputs": [
    {
      "id": "weight_kg",
      "label": "Weight Lifted",
      "type": "number",
      "unit": "kg",
      "default": 100,
      "min": 1,
      "max": 500,
      "step": 0.5
    },
    {
      "id": "reps",
      "label": "Reps",
      "type": "number",
      "unit": "reps",
      "default": 5,
      "min": 1,
      "max": 20,
      "step": 1
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 100,
      "reps": 5
    },
    "expected_output": "116.7 kg"
  },
  "result_summary_template": "Lifting {weight_kg} for {reps} repetitions, the Epley formula estimates a one-rep max of {result}.",
  "methodology": "Applies the Epley (1985) formula: 1RM = weight × (1 + reps / 30). This linear model estimates one-repetition maximum from submaximal lift performance, using a constant divisor of 30 to scale the repetition factor.",
  "sources": [
    {
      "label": "Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: University of Nebraska Press; 1985.",
      "url": "https://www.nsca.com/education/tools-and-resources/load-rep-calculators/"
    },
    {
      "label": "LeSuer DA, McCormick JH, Mayhew JL, et al. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997;11(4):211-213.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/27834588/"
    },
    {
      "label": "National Strength and Conditioning Association. NSCA's Essentials of Personal Training, 2nd Edition. Champaign, IL: Human Kinetics; 2011.",
      "url": "https://www.nsca.com/"
    }
  ],
  "faqs": [
    {
      "question": "What is the Epley formula used for?",
      "answer": "The Epley formula estimates one-repetition maximum (1RM) from a set of multiple repetitions performed at a submaximal load. It is commonly used in strength training to predict maximal strength without requiring a true maximal lift."
    },
    {
      "question": "Why does the formula use a divisor of 30?",
      "answer": "The constant 30 in the Epley formula reflects an empirical observation that each additional repetition corresponds to approximately 3.33% of the load. This linear scaling factor was derived from analysis of submaximal and maximal lift data in trained populations."
    },
    {
      "question": "How accurate is the Epley formula?",
      "answer": "Accuracy is highest for repetition ranges of 2–10 in compound barbell exercises. Beyond 10 reps, the formula may underestimate true 1RM because muscular endurance begins to dominate performance. Individual variation in fiber type, training history, and lifting technique also affects precision."
    },
    {
      "question": "Can this calculator be used for all exercises?",
      "answer": "The Epley formula was developed primarily for multi-joint barbell movements like the squat, bench press, and deadlift. It may be less accurate for isolation exercises, machine-based movements, or bodyweight exercises where leverage and stabilization demands differ."
    },
    {
      "question": "Is a calculated 1RM the same as a tested 1RM?",
      "answer": "No. A calculated 1RM is a mathematical estimate based on submaximal performance. Actual 1RM testing involves lifting maximal loads and is influenced by neural coordination, arousal, and skill under heavy loads—factors not captured by prediction equations."
    }
  ],
  "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-comparison",
      "title": "Multi-Formula 1RM Comparison Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/one-rep-max-comparison.json",
      "page_url": "https://fitmetriclab.com/en/tools/strength-training/one-rep-max-comparison/"
    },
    {
      "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."
}