{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"mass"},"result":{"entity_type":"calculator","id":"mass","calculator_id":"mass","canonical_url":"https://tttkmbb.com/conversion/mass","name":"Mass / Weight Converter","title":"Weight and Mass Converter – Kilograms, Grams, Pounds, Ounces, Stones and Tons","category":"conversion","category_name":"Unit Conversion","tool_name":"convert_mass","featured_mcp_tool":false,"description":"Converts mass between metric units (μg to tonne), avoirdupois units (grain, oz, lb, stone, short and long ton) and carats using the exact definition 1 lb = 0.45359237 kg.","use_when":"You need body weight, ingredient weight or freight mass in another unit, e.g. pounds to kilograms, ounces to grams or stones to pounds.","do_not_use_when":"You need to convert weight to volume (needs a density; use density) or to force in newtons (use force).","inputs":[{"name":"value","label":"Value","type":"number","required":true,"description":"Amount to convert, expressed in from_unit.","example":150},{"name":"from_unit","label":"From unit","type":"enum","required":true,"values":[{"value":"ug","label":"Microgram (μg)","aliases":["μg","microgram","micrograms","mcg"]},{"value":"mg","label":"Milligram (mg)","aliases":["milligram","milligrams","milligramme"]},{"value":"g","label":"Gram (g)","aliases":["gram","grams","gramme","grammes","gm"]},{"value":"kg","label":"Kilogram (kg)","aliases":["kilogram","kilograms","kilogramme","kilogrammes","kilo","kilos","kgs"]},{"value":"t","label":"Tonne (t)","aliases":["tonne","tonnes","metric ton","metric-ton","metricton","metric·ton","metric_ton","metric tons","metric-tons","metrictons","metric·tons","metric_tons","ton (metric)","ton-(metric)","ton(metric)","ton·(metric)","ton_(metric)"]},{"value":"grain","label":"Grain (grain)","aliases":["grains"]},{"value":"oz","label":"Ounce (oz)","aliases":["ounce","ounces","avoirdupois ounce","avoirdupois-ounce","avoirdupoisounce","avoirdupois·ounce","avoirdupois_ounce","oz av","oz-av","ozav","oz·av","oz_av"]},{"value":"lb","label":"Pound (lb)","aliases":["pound","pounds","lbs","lbm","pound mass","pound-mass","poundmass","pound·mass","pound_mass"]},{"value":"st","label":"Stone (st)","aliases":["stone","stones"]},{"value":"ton_us","label":"Short ton (ton_us)","aliases":["ton-us","ton us","tonus","ton·us","short ton","short-ton","shortton","short·ton","short_ton","short tons","short-tons","shorttons","short·tons","short_tons","us ton","us-ton","uston","us·ton","us_ton","us tons","us-tons","ustons","us·tons","us_tons","ton (us)","ton-(us)","ton(us)","ton·(us)","ton_(us)","ton","tons"]},{"value":"ton_uk","label":"Long ton (ton_uk)","aliases":["ton-uk","ton uk","tonuk","ton·uk","long ton","long-ton","longton","long·ton","long_ton","long tons","long-tons","longtons","long·tons","long_tons","uk ton","uk-ton","ukton","uk·ton","uk_ton","uk tons","uk-tons","uktons","uk·tons","uk_tons","imperial ton","imperial-ton","imperialton","imperial·ton","imperial_ton","ton (uk)","ton-(uk)","ton(uk)","ton·(uk)","ton_(uk)"]},{"value":"ct","label":"Carat (ct)","aliases":["carat","carats","metric carat","metric-carat","metriccarat","metric·carat","metric_carat"]}],"description":"Unit of the input value. 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Accepted symbols: ug, mg, g, kg, t, grain, oz, lb, st, ton_us, ton_uk, ct; spelled-out names and common abbreviations are accepted too.","type":"string","enum":["ug","mg","g","kg","t","grain","oz","lb","st","ton_us","ton_uk","ct"],"examples":["lb"]},"to_unit":{"description":"Unit to convert into (same symbols as from_unit).","type":"string","enum":["ug","mg","g","kg","t","grain","oz","lb","st","ton_us","ton_uk","ct"],"examples":["kg"]}},"additionalProperties":false,"required":["value","from_unit","to_unit"]},"output_schema":{"type":"object","properties":{"result":{"description":"Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).","type":"number"},"result_text":{"description":"The conversion as text with 6 significant figures, e.g. \"5 mi = 8.04672 km\".","type":"string"},"formula":{"description":"Relation used, e.g. \"1 mi = 1.609344 km\".","type":"string"},"factor":{"description":"Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.","type":"number"},"conversion_table":{"description":"The input value expressed in every supported mass unit (6 significant figures), keyed by unit symbol.","type":"object"}}},"formula":"result = value × factor, factor = (1 from_unit in kg) / (1 to_unit in kg)","sources":[{"name":"NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors","url":"https://www.nist.gov/pml/special-publication-811","type":"standard","retrieved_at":"2026-09-23"},{"name":"BIPM – The International System of Units (SI Brochure, 9th edition)","url":"https://www.bipm.org/en/publications/si-brochure","type":"standard","retrieved_at":"2026-09-23"},{"name":"Wikipedia – Conversion of units","url":"https://en.wikipedia.org/wiki/Conversion_of_units","type":"reference","retrieved_at":"2026-09-23"}],"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":"150 pounds to kilograms","inputs":{"value":150,"from_unit":"lb","to_unit":"kg"},"expected":{"result":68.038856,"factor":0.45359237,"formula":"1 lb = 0.45359237 kg","conversion_table":{"st":10.7143,"g":68038.9}},"url":"https://tttkmbb.com/api/v1/calculate/mass?value=150&from_unit=lb&to_unit=kg"},{"name":"2.5 kg to ounces","inputs":{"value":2.5,"from_unit":"kg","to_unit":"oz"},"expected":{"result":88.184905,"conversion_table":{"lb":5.51156,"g":2500}},"url":"https://tttkmbb.com/api/v1/calculate/mass?value=2.5&from_unit=kg&to_unit=oz"}],"faq":[{"q":"Which ton does 'ton' mean?","a":"The plain alias 'ton' resolves to the US short ton (2000 lb = 907.18474 kg). Use ton_uk for the long ton (2240 lb) and t for the metric tonne (1000 kg)."},{"q":"Is an ounce the same as a fluid ounce?","a":"No. The ounce here is the avoirdupois mass unit (28.349523125 g); fluid ounces are volume units handled by the volume and cooking-measurements calculators."},{"q":"Weight or mass?","a":"Everyday 'weight' in kg or lb is mass. The gravitational force on that mass (kgf, lbf, N) is handled by the force converter."}],"tags":["weight converter","mass converter","pounds to kg","ounces to grams","stone to pounds"],"related":[{"calculator_id":"density","reason":"Convert between mass and volume with a density."},{"calculator_id":"force","reason":"Mass to weight-force (kgf, lbf, N)."},{"calculator_id":"bmi","reason":"Use the converted body weight in kg."}],"links":{"html":"https://tttkmbb.com/conversion/mass","markdown":"https://tttkmbb.com/conversion/mass.md","json":"https://tttkmbb.com/conversion/mass.json","api":"https://tttkmbb.com/api/v1/calculate/mass","schema":"https://tttkmbb.com/api/v1/calculators/mass","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:23:13Z"}