Home › Unit Conversion › Mass / Weight Converter

Mass / Weight Converter

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.

When to use

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).

Formula

result = value × factor, factor = (1 from_unit in kg) / (1 to_unit in kg)

Inputs

Parameter	Type	Required	Description
`value`	number	yes	Amount to convert, expressed in from_unit.
`from_unit`	enum: ug \| mg \| g \| kg \| t \| grain \| oz \| lb \| st \| ton_us \| ton_uk \| ct	yes	Unit of the input value. 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.
`to_unit`	enum: ug \| mg \| g \| kg \| t \| grain \| oz \| lb \| st \| ton_us \| ton_uk \| ct	yes	Unit to convert into (same symbols as from_unit).

Outputs

Output	Type	Description
`result`	number	Converted value expressed in to_unit (rounded to 6 decimals; see result_text for very small or very large values).
`result_text`	string	The conversion as text with 6 significant figures, e.g. "5 mi = 8.04672 km".
`formula`	string	Relation used, e.g. "1 mi = 1.609344 km".
`factor`	number	Multiplier from from_unit to to_unit (result = value × factor); absent for non-linear conversions.
`conversion_table`	object	The input value expressed in every supported mass unit (6 significant figures), keyed by unit symbol.

Example

150 pounds to kilograms: {"value":150,"from_unit":"lb","to_unit":"kg"} → {"result":68.038856,"factor":0.45359237,"formula":"1 lb = 0.45359237 kg","conversion_table":{"st":10.7143,"g":68038.9}}

2.5 kg to ounces: {"value":2.5,"from_unit":"kg","to_unit":"oz"} → {"result":88.184905,"conversion_table":{"lb":5.51156,"g":2500}}

GET https://tttkmbb.com/api/v1/calculate/mass?value=150&from_unit=lb&to_unit=kg

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/mass (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/mass · Markdown: https://tttkmbb.com/conversion/mass.md · JSON definition: https://tttkmbb.com/conversion/mass.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="mass"
OpenAPI operationId: convert_mass
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Which ton does 'ton' mean?

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).

Is an ounce the same as a fluid ounce?

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.

Weight or mass?

Everyday 'weight' in kg or lb is mass. The gravitational force on that mass (kgf, lbf, N) is handled by the force converter.

Related calculators

Density Converter — Convert between mass and volume with a density.
Force Converter — Mass to weight-force (kgf, lbf, N).
BMI Calculator — Use the converted body weight in kg.