Available Mass units

• kilogram conversions

  The kilogram is the SI base unit of mass. It is used globally as the standard for measuring weight and mass in science, industry, trade, and everyday life.

• gram conversions

  A gram is a metric unit of mass equal to one thousandth of a kilogram. It is widely used in cooking, food labelling, and the measurement of small quantities in science and pharmacy.

• pound conversions

  A pound is a unit of mass in imperial and US customary systems equal to 16 ounces. It is widely used in the United States for body weight, grocery shopping, and general weight measurement.

• ounce conversions

  An ounce is a unit of mass in imperial and US customary systems equal to approximately 28.35 grams. It is frequently used in cooking, food portioning, and the measurement of precious metals.

• tonne conversions

  A tonne, also known as a metric ton, is a unit of mass equal to 1,000 kilograms. It is used in industrial shipping, cargo measurement, and large-scale material production and trade.

• milligram conversions

  A milligram is a metric unit of mass equal to one thousandth of a gram. It is commonly used in pharmaceutical dosing, nutritional content labelling, and laboratory chemistry.

• microgram conversions

  A microgram is a metric unit of mass equal to one millionth of a gram. It is used in analytical chemistry, toxicology, pharmacology, and measuring trace amounts of substances in laboratory settings.

• stone conversions

  A stone is a unit of mass used primarily in the United Kingdom and Ireland, equal to 14 pounds. It is mainly used to express human body weight in everyday conversation.

• short ton (US) conversions

  A short ton is a unit of mass used primarily in the United States, equal to 2,000 pounds. It is used in industries such as mining, agriculture, and freight transportation.

• long ton (UK) conversions

  A long ton is a unit of mass historically used in the United Kingdom, equal to 2,240 pounds. It is used in shipping, naval architecture, and some industrial contexts in the UK.

Full Mass conversion matrix

About Mass

Units of mass and weight

Real-world uses

Mass measurements are critical across cooking, medicine, commerce, and science. Pharmacists dose medications in milligrams, bakers weigh flour in grams, and freight companies bill by the tonne. In aerospace, every gram matters for fuel efficiency, while jewellers trade in carats and troy ounces. Agricultural commodities like wheat and coffee are priced per metric tonne on global exchanges, making accurate mass conversion essential to international trade.

History

The oldest known standardised weights date to the Indus Valley civilisation around 2600 BCE, using carefully shaped stone cubes. Medieval Europe relied on the grain (the weight of a barley grain) as a base unit. The metric kilogram was introduced in 1795 as the mass of one litre of water. For over a century, it was defined by a platinum-iridium cylinder kept in Paris, until 2019 when the kilogram was redefined in terms of the Planck constant.

Common mistakes

The most common confusion is between mass and weight: mass is an intrinsic property measured in kilograms, while weight is a force measured in newtons. People also frequently confuse the troy ounce used for precious metals (31.1 g) with the avoirdupois ounce used for everyday goods (28.35 g). Another error is assuming that a UK ton and a US ton are the same — they differ by about 1.6%.

Measurement standards

The kilogram is defined by fixing the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule-seconds, as established at the 26th General Conference on Weights and Measures in 2018. This ended the last SI definition based on a physical artefact.

Did you know?

The International Prototype of the Kilogram, a platinum-iridium cylinder stored near Paris since 1889, was found to have drifted by about 50 micrograms relative to its copies over a century — roughly the mass of a fingerprint.

Common values