Science, Tech, Math › Science Gram Definition and Examples in Science What Is a Gram? Share Flipboard Email Print A gram is small unit of mass that is one-thousandth of a kilogram. Thatree Thitivongvaroon, Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 04, 2019 A gram is a unit of mass in the metric system defined as one thousandth (1 x 10-3) of a kilogram. Originally, the gram was defined as a unit equal to the mass of one cubic centimeter of pure water at 4°C (the temperature at which water has maximum density). The definition was changed when the base units for the International System of Units (SI) were redefined by the 26th General Conference of Weights and Measures. The change went into effect May 20, 2019. The symbol for the gram is the lowercase letter "g." Incorrect symbols include "gr" (the symbol for grains), "Gm" (the symbol for the gigameter), and "gm" (easily confused with the symbol for the gram-meter, g⋅m). Gram may also be spelled gramme. Key Takeaways: Gram Definition The gram is a unit of mass.One gram is one thousandth the mass of one kilogram. The previous definition of the gram was the absolute weight of a 1-centimeter cube of pure water at 4 °C.The symbol for the gram is g.The gram is a small unit of mass. It is approximately the mass of one small paper clip. Examples of Gram Weight Because a gram is a small unit of weight, its size may be difficult for many people to visualize. Here are common examples of objects that have about one gram of mass: A small paperclipA thumbtackA piece of chewing gumOne US billA pen capOne cubic centimeter (milliliter) of waterA quarter teaspoon of sugar Useful Gram Conversion Factors Grams may be converted into several other units of measurement. Some common conversion factors include: 1 gram (1 g) = 5 carats (5 ct)1 gram (1 g) = 10-3 kilograms (10-3 kg)1 gram (1 g) = 15.43236 grains (gr)1 troy ounce (ozt) = 31.1035 g1 gram = 8.98755179×1013 joules (J)500 grams = 1 Jin (Chinese unit of measurement)1 avoirdupois ounce (oz) = 28.3495 grams (g) Uses of the Gram The gram is widely used in science, particular chemistry and physics. Outside of the United States, the gram is used to measure non-liquid cooking ingredients and produce (e.g., flour, sugar, bananas). Relative composition for food nutrition labels is stated per 100 grams of product, even within the United States. History of the Gram In 1795, the French National Convention replaced the gravet with the gramme in the metric system. While the term changed, the definition remained that of the weight of one cubic centimeter of water. The word gramme came from the Latin word gramma which in turn derived from the Greek word grámma. The grámma was a unit used in Late Antiquity (around the 4th century AD) equal to two oboli (Greek coins) or one twenty-fourth part of an ounce. The gram was a fundamental unit of mass in the centimeter-gram-second (CGS) system in the 19th century. The meter-kilogram-second (MKS) system of units was proposed in 1901, but the CGS and MKS systems co-exists throughout the early to mid 20th century. The MKS system became the system of base units in 1960. However, the gram was still defined based on the mass of water. In 2019, the gram was defined based on the kilogram. The kilogram has a mass almost exactly equal to that of one liter of water, but its definition has been refined, too. In 2018, Planck's constant was defined. This allowed definition of the kilogram in terms of the second and the meter. Planck's constant h is defined to be 6.62607015×10−34 and equal to one kilogram meter squared per second (kg⋅m2⋅s−1). Even so, standard masses for the kilogram still exist and are used as secondary standards for kilogram and gram weights. For all practical purposes, a liter of pure water has a mass of one kilogram and a milliliter of pure water has the mass of one gram. Sources Materese, Robin (November 16, 2018). "Historic Vote Ties Kilogram and Other Units to Natural Constants". NIST. National Institute of Standards and Technology (October 2011). Butcher, Tina; Cook, Steve; Crown, Linda et al. eds. "Appendix C – General Tables of Units of Measurement" Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. NIST Handbook. 44 (2012 ed.). Washington, D.C.: U.S. Department of Commerce, Technology Administration, National Institute of Standards and Technology. ISSN 0271-4027.