|Unit system:||SI derived unit|
|1 g in...||is equal to...|
|SI base units||10-3 kilograms|
|CGS units||1 gram|
|U.S. customary||0.0353 ounces|
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.
Symbol and abbreviations 
The International System of Units (SI) unit symbol for the gram is "g" following the numeric value with a space, as in "640 g". While some authors use ad-hoc abbreviations, this creates confusion. For example, the use of abbreviations such as "gm", "Gm", or "GM" for grams could potentially lead to serious errors in health-care settings where accidentally transposing "gm" to "mg" (milligrams) could result in a 1,000 times dosage error. It is therefore important to use "g" as specified in the SI standard to avoid confusion or misunderstanding.
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.
Conversion factors 
- 1 gram (g) = 15.4323583529 grains (gr)
- 1 grain (gr) = 0.06479891 grams (g)
- 1 avoirdupois ounce (oz) = 28.349523125 grams (g)
- 1 troy ounce (ozt) = 31.1034768 grams (g)
- 1 gram (g) = 8.98755179×1013 joules (J) (by mass–energy equivalence)
- 1 gram is roughly equal to 1 small paper clip or pen cap.
- The Japanese 1 yen coin has a mass of one gram. (lighter than the British penny (3.56 g), the United States cent (2.5 g) or the "Euro-cent" (2.30 g)).
See also 
- "Weights and Measures Act 1985 (c. 72)". The UK Statute Law Database. Office of Public Sector Information. Retrieved 2011-01-26. "§92."
- Décret relatif aux poids et aux mesures, 1795
- "Circulating Coin Designs". Japan Mint. Retrieved 7 March 2010.