The gram (often gramme in British English), (Greek/Latin root grámma); symbol g, is a unit of mass.

Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre, and at the temperature of melting ice" (later 4 °C), a gram is now defined as one one-thousandth of the SI base unit, the kilogram, or 1×10^-3 kg, which itself is defined as being equal to the mass of a physical prototype preserved by the International Bureau of Weights and Measures.

Other abbreviations

The International System of Units abbreviation for the gram is g, and follows the numeric value with a space, as in "640 g". In some fields and regions, the international standard units for units are used quite strictly, in particular in technical and scientific publications and in legally regulated product labels. In other contexts, a wide range of other unofficial abbreviations have been encountered, such as gr, gm, grm, gms, grms. The use of abbreviations such as "gm", "Gm", or "GM" for grams could potentially lead to serious errors in healthcare settings where accidentally transposing "gm" to "mg" (milligrams) would result in a 1000 times dosage difference. It would therefore be prudent to use "g" as the abbreviation for grams in any healthcare setting.

History

It was the base unit of mass in the original French metric system and the later centimetre-gram-second (CGS) system of units. The word originates from late Latin gramma – a small weight.

Uses

The gram is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide. For food products that are typically sold in quantities far less than 1 kg, the unit price is normally given per 100 g.

Most standards and legal requirements for nutrition labels on food products require relative contents to be stated per 100 g of the product, such that the resulting figure can also be read as a percentage.

SI multiples

Because SI prefixes may not be concatenated (serially linked) within the name or symbol for a unit of measure, SI prefixes are used with the gram, not the kilogram, which already has a prefix as part of its name.NIST: SI prefixes (link to Web site).  For instance, one-millionth of a kilogram is 1 mg (one milligram), not 1 µkg (one microkilogram).

• When the Greek lowercase “µ”

(mu) in the symbol of microgram is typographically unavailable, it is occasionally—although not properly—replaced by Latin lowercase “u”.