{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"katch-mcardle-bmr"},"result":{"entity_type":"calculator","id":"katch-mcardle-bmr","calculator_id":"katch-mcardle-bmr","canonical_url":"https://tttkmbb.com/fitness/katch-mcardle-bmr","name":"Katch-McArdle BMR Calculator","title":"Katch-McArdle BMR Calculator – Resting Metabolic Rate from Lean Body Mass, with TDEE","category":"fitness","category_name":"Sports & Fitness","tool_name":"calculate_katch_mcardle_bmr","featured_mcp_tool":false,"description":"Estimates basal metabolic rate with the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass in kg), which uses body-fat percentage instead of height, sex and age, and multiplies it by a standard activity factor for total daily energy expenditure.","use_when":"You know body-fat percentage (especially for lean or very muscular people, whom weight-based equations misestimate) and want resting and daily calorie needs.","do_not_use_when":"Body-fat percentage is unknown or guessed (use bmr / tdee with Mifflin-St Jeor instead), or for children, pregnancy or clinical nutrition; informational, not medical advice.","inputs":[{"name":"weight_kg","label":"Weight","type":"number","unit":"kg","required":true,"max":400,"exclusive_min":0,"description":"Body weight in kilograms.","example":80},{"name":"body_fat_percent","label":"Body fat","type":"number","unit":"%","required":true,"min":2,"max":70,"description":"Body-fat percentage (calipers, DEXA, BIA or a tape-measure estimate).","example":15},{"name":"activity_level","label":"Activity level","type":"enum","required":false,"default":"sedentary","values":[{"value":"sedentary","label":"Sedentary (little or no exercise) ×1.2"},{"value":"light","label":"Light (1–3 days/week) ×1.375","aliases":["lightly active"]},{"value":"moderate","label":"Moderate (3–5 days/week) ×1.55","aliases":["moderately active"]},{"value":"active","label":"Active (6–7 days/week) ×1.725","aliases":["very"]},{"value":"very_active","label":"Very active (physical job or twice-daily training) ×1.9","aliases":["extra active","athlete"]}],"description":"Weekly exercise level; maps to the standard multipliers 1.2 / 1.375 / 1.55 / 1.725 / 1.9.","example":"moderate"}],"outputs":[{"name":"lean_body_mass_kg","label":"Lean body mass","type":"number","unit":"kg","decimals":1,"description":"weight_kg × (1 − body_fat_percent / 100)."},{"name":"fat_mass_kg","label":"Fat mass","type":"number","unit":"kg","decimals":1,"description":"weight_kg × body_fat_percent / 100."},{"name":"bmr_kcal","label":"BMR (Katch-McArdle)","type":"number","unit":"kcal/day","decimals":1,"description":"370 + 21.6 × lean body mass."},{"name":"bmr_kj","label":"BMR (kJ)","type":"number","unit":"kJ/day","decimals":0,"description":"bmr_kcal × 4.184."},{"name":"activity_multiplier","label":"Activity multiplier","type":"number","decimals":3,"description":"Factor applied to BMR for the chosen activity level."},{"name":"tdee_kcal","label":"TDEE","type":"number","unit":"kcal/day","decimals":1,"description":"bmr_kcal × activity_multiplier: estimated maintenance calories."}],"input_schema":{"type":"object","properties":{"weight_kg":{"description":"Body weight in kilograms. Unit: kg.","type":"number","maximum":400,"exclusiveMinimum":0,"examples":[80],"x-unit":"kg"},"body_fat_percent":{"description":"Body-fat percentage (calipers, DEXA, BIA or a tape-measure estimate). Unit: %.","type":"number","minimum":2,"maximum":70,"examples":[15],"x-unit":"%"},"activity_level":{"description":"Weekly exercise level; maps to the standard multipliers 1.2 / 1.375 / 1.55 / 1.725 / 1.9.","type":"string","enum":["sedentary","light","moderate","active","very_active"],"default":"sedentary","examples":["moderate"]}},"additionalProperties":false,"required":["weight_kg","body_fat_percent"]},"output_schema":{"type":"object","properties":{"lean_body_mass_kg":{"description":"weight_kg × (1 − body_fat_percent / 100). Unit: kg.","type":"number","x-unit":"kg"},"fat_mass_kg":{"description":"weight_kg × body_fat_percent / 100. Unit: kg.","type":"number","x-unit":"kg"},"bmr_kcal":{"description":"370 + 21.6 × lean body mass. Unit: kcal/day.","type":"number","x-unit":"kcal/day"},"bmr_kj":{"description":"bmr_kcal × 4.184. Unit: kJ/day.","type":"number","x-unit":"kJ/day"},"activity_multiplier":{"description":"Factor applied to BMR for the chosen activity level.","type":"number"},"tdee_kcal":{"description":"bmr_kcal × activity_multiplier: estimated maintenance calories. Unit: kcal/day.","type":"number","x-unit":"kcal/day"}}},"formula":"lean_body_mass_kg = weight_kg × (1 − body_fat_percent / 100); bmr_kcal = 370 + 21.6 × lean_body_mass_kg; bmr_kj = bmr_kcal × 4.184; tdee_kcal = bmr_kcal × activity multiplier (sedentary 1.2, light 1.375, moderate 1.55, active 1.725, very_active 1.9)","method":"The Katch-McArdle equation (McArdle, Katch & Katch, Exercise Physiology; closely related to Cunningham's 1980 equation 500 + 22 × LBM) predicts resting energy from fat-free mass alone, so it is independent of sex and age; its accuracy is bounded by the accuracy of the body-fat estimate. Informational, not medical advice.","sources":[{"name":"Wikipedia – Basal metabolic rate (Katch-McArdle formula)","url":"https://en.wikipedia.org/wiki/Basal_metabolic_rate","type":"reference","retrieved_at":"2026-09-24"},{"name":"FAO/WHO/UNU (2004) Human energy requirements – physical activity levels","url":"https://www.fao.org/4/y5686e/y5686e00.htm","type":"standard","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"80 kg, 15 % body fat, moderate activity","inputs":{"weight_kg":80,"body_fat_percent":15,"activity_level":"moderate"},"expected":{"lean_body_mass_kg":68,"bmr_kcal":1838.8,"bmr_kj":7694,"activity_multiplier":1.55,"tdee_kcal":2850.1},"url":"https://tttkmbb.com/api/v1/calculate/katch-mcardle-bmr?weight_kg=80&body_fat_percent=15&activity_level=moderate"},{"name":"65 kg, 28 % body fat, sedentary","inputs":{"weight_kg":65,"body_fat_percent":28},"expected":{"lean_body_mass_kg":46.8,"bmr_kcal":1380.9,"tdee_kcal":1657.1},"url":"https://tttkmbb.com/api/v1/calculate/katch-mcardle-bmr?weight_kg=65&body_fat_percent=28"}],"faq":[{"q":"When is Katch-McArdle better than Mifflin-St Jeor?","a":"When body-fat percentage is measured reasonably well and the person is unusually lean or muscular; for typical adults with only weight and height, Mifflin-St Jeor is at least as accurate."},{"q":"Why is there no sex or age input?","a":"Sex and age mostly affect resting metabolism through their effect on lean mass, which this formula takes directly."}],"tags":["katch mcardle","bmr from lean body mass","resting metabolic rate","tdee body fat","lean mass calories"],"related":[{"calculator_id":"bmr","reason":"Mifflin-St Jeor and Harris-Benedict estimates without body fat."},{"calculator_id":"tdee","reason":"Calorie targets for loss or gain from a weight-based BMR."},{"calculator_id":"skinfold-body-fat","reason":"Caliper body-fat percentage for this formula."}],"links":{"html":"https://tttkmbb.com/fitness/katch-mcardle-bmr","markdown":"https://tttkmbb.com/fitness/katch-mcardle-bmr.md","json":"https://tttkmbb.com/fitness/katch-mcardle-bmr.json","api":"https://tttkmbb.com/api/v1/calculate/katch-mcardle-bmr","schema":"https://tttkmbb.com/api/v1/calculators/katch-mcardle-bmr","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:51:43Z"}