{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"lean-body-mass"},"result":{"entity_type":"calculator","id":"lean-body-mass","calculator_id":"lean-body-mass","canonical_url":"https://tttkmbb.com/health/lean-body-mass","name":"Lean Body Mass Calculator","title":"Lean Body Mass Calculator – Boer, James and Hume Formulas","category":"health","category_name":"Health","tool_name":"calculate_lean_body_mass","featured_mcp_tool":false,"description":"Estimates lean body mass (fat-free mass) from weight, height and sex with the Boer (1984), James (1976) and Hume (1966) formulas.","use_when":"You need fat-free mass for drug dosing, nutrition planning or as a body-composition reference without a scan.","do_not_use_when":"You have measured body-fat percentage (lean mass = weight × (1 − body fat) is then more accurate) or the person is a child.","inputs":[{"name":"sex","label":"Biological sex","type":"enum","required":true,"values":[{"value":"male","label":"Male","aliases":["m","man"]},{"value":"female","label":"Female","aliases":["f","woman"]}],"description":"Biological sex used to select the formula coefficients.","example":"male"},{"name":"weight_kg","label":"Weight","type":"number","unit":"kg","required":true,"max":700,"exclusive_min":0,"description":"Body weight in kilograms.","example":70},{"name":"height_cm","label":"Height","type":"number","unit":"cm","required":true,"min":50,"max":300,"description":"Height in centimetres.","example":175}],"outputs":[{"name":"boer_kg","label":"Boer","type":"number","unit":"kg","decimals":1,"description":"Boer (1984) formula, commonly used for anaesthetic dosing."},{"name":"james_kg","label":"James","type":"number","unit":"kg","decimals":1,"description":"James (1976) formula."},{"name":"hume_kg","label":"Hume","type":"number","unit":"kg","decimals":1,"description":"Hume (1966) formula."},{"name":"boer_body_fat_percent","label":"Implied body fat (Boer)","type":"number","unit":"%","decimals":1,"description":"100 × (1 − boer_kg / weight_kg)."}],"input_schema":{"type":"object","properties":{"sex":{"description":"Biological sex used to select the formula coefficients.","type":"string","enum":["male","female"],"examples":["male"]},"weight_kg":{"description":"Body weight in kilograms. Unit: kg.","type":"number","maximum":700,"exclusiveMinimum":0,"examples":[70],"x-unit":"kg"},"height_cm":{"description":"Height in centimetres. Unit: cm.","type":"number","minimum":50,"maximum":300,"examples":[175],"x-unit":"cm"}},"additionalProperties":false,"required":["sex","weight_kg","height_cm"]},"output_schema":{"type":"object","properties":{"boer_kg":{"description":"Boer (1984) formula, commonly used for anaesthetic dosing. Unit: kg.","type":"number","x-unit":"kg"},"james_kg":{"description":"James (1976) formula. Unit: kg.","type":"number","x-unit":"kg"},"hume_kg":{"description":"Hume (1966) formula. Unit: kg.","type":"number","x-unit":"kg"},"boer_body_fat_percent":{"description":"100 × (1 − boer_kg / weight_kg). Unit: %.","type":"number","x-unit":"%"}}},"formula":"Boer: male 0.407·W + 0.267·H − 19.2, female 0.252·W + 0.473·H − 48.3. James: male 1.1·W − 128·(W/H)², female 1.07·W − 148·(W/H)². Hume: male 0.32810·W + 0.33929·H − 29.5336, female 0.29569·W + 0.41813·H − 43.2933. W in kg, H in cm.","sources":[{"name":"Boer P (1984) Estimated lean body mass as an index for normalization of body fluid volumes in humans, Am J Physiol 247:F632-636","url":"https://pubmed.ncbi.nlm.nih.gov/6496691/","type":"peer_reviewed","retrieved_at":"2026-09-24"},{"name":"Hume R (1966) Prediction of lean body mass from height and weight, J Clin Pathol 19:389-391","url":"https://pubmed.ncbi.nlm.nih.gov/5929341/","type":"peer_reviewed","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":"Male, 70 kg, 175 cm","inputs":{"sex":"male","weight_kg":70,"height_cm":175},"expected":{"boer_kg":56,"james_kg":56.5,"hume_kg":52.8,"boer_body_fat_percent":20},"url":"https://tttkmbb.com/api/v1/calculate/lean-body-mass?sex=male&weight_kg=70&height_cm=175"},{"name":"Female, 60 kg, 165 cm","inputs":{"sex":"female","weight_kg":60,"height_cm":165},"expected":{"boer_kg":44.9,"james_kg":44.6,"hume_kg":43.4},"url":"https://tttkmbb.com/api/v1/calculate/lean-body-mass?sex=female&weight_kg=60&height_cm=165"}],"faq":[{"q":"Which formula should I use?","a":"Boer is the most common in clinical dosing; James overestimates in obesity; Hume is older. Differences of 2–4 kg are typical."}],"tags":["lean body mass","fat free mass","lbm","boer","james","hume"],"related":[{"calculator_id":"body-fat","reason":"Measure-based body fat and lean mass."}],"links":{"html":"https://tttkmbb.com/health/lean-body-mass","markdown":"https://tttkmbb.com/health/lean-body-mass.md","json":"https://tttkmbb.com/health/lean-body-mass.json","api":"https://tttkmbb.com/api/v1/calculate/lean-body-mass","schema":"https://tttkmbb.com/api/v1/calculators/lean-body-mass","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-23T23:33:47Z","next_actions":[{"tool":"run_calculator","calculator_id":"lean-body-mass","reason":"Run Lean Body Mass Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/health/lean-body-mass.md"}}