gram-molecular weight, amount of a molecular substance whose weight, in grams, is numerically equal to the molecular weight of that substance. For example, one gram-molecular weight of molecular oxygen, O₂ (molecular weight approximately 32), is 32 grams, and one gram-molecular weight of water, H₂O (molecular weight approximately 18) is 18 grams. The term mole is often used in place of gram-molecular weight. See gram-atomic weight.

gram-molecular volume, the volume occupied by one gram-molecular weight of any substance at STP. See molar volume.

gram-calorie: see calorie.

gram-atomic weight, amount of an atomic substance whose weight, in grams, is numerically equal to the atomic weight of that substance. For example, 1 gram-atomic weight of atomic oxygen, O (atomic weight approximately 16), is 16 grams. See gram-molecular weight.

gram, abbr. g, unit of mass equal to 0.001 kilogram, the basic unit of mass in the metric system. The gram is the unit of mass in the cgs system. It is approximately equal to 0.035 avoirdupois ounce, or 0.0022 pound; a 1-pound mass equals about 453.6 grams.

Unit of energy or heat. Various precise definitions are used for different purposes (physical chemistry measurements, engineering steam tables, and thermochemistry), but in all cases the calorie is about 4.2 joules, the amount of heat needed to raise the temperature of 1 g of water by 1 °C (1.8 °F) at normal atmospheric pressure. The calorie used by dietitians and food scientists and found on food labels is actually the kilocalorie (also called Calorie and abbreviated kcal or Cal), or 1,000 calories. It is a measure of the amount of heat energy or metabolic energy contained in the chemical bonds (see bonding) of a food.

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Unit of mass or weight used especially in the centimetre-gram-second (CGS) system of measurement. One gram is equal to 0.001 kg, about 0.035 oz, or 15.43 grains. The gram is very nearly equal to the mass of 1 cc of pure water at its maximum density. The gram of force is equal to the weight of a gram of mass under standard gravity. For greater precision, the mass may be weighed at a point at which the acceleration due to gravity is 980.655 cm/sec². Seealso gravitation; metric system.

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