avoirdupois weight

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1. heaviness; the degree to which a body is drawn toward the earth by gravity. (See also Tables of Weights and Measures in the Appendix.) Abbreviated wt.
2. in statistics, the process of assigning greater importance to some observations than to others, or a mathematical factor used to apply such a process.
apothecaries' weight see apothecaries' system.
atomic weight the sum of the masses of the constituents of an atom, expressed in atomic mass units (or daltons), in SI units (i.e., kilograms), or as a dimensionless ratio derived by comparing the mass to the mass of an atom of carbon-12, which is taken as 12.000. Abbreviated At wt.
avoirdupois weight see avoirdupois system.
equivalent weight the amount of substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen), usually expressed in grams; for acid/base reactions, one equivalent donates or receives a mole of protons and the equivalent weight is the ratio of the molecular weight to the number of protons involved in the reaction. For oxidation-reduction reactions, one equivalent donates or receives a mole of electrons and the equivalent weight is the ratio of the molecular weight to the number of electrons involved in the reaction.
gram molecular weight the molecular weight of a substance expressed in grams; one gram molecular weight of a molecular substance contains one mole of molecules. See also mole1.
low birth weight (LBW) see under infant.
molecular weight the weight of a molecule of a chemical compound as compared with the weight of an atom of carbon-12; it is equal to the sum of the weights of its constituent atoms and is dimensionless. Abbreviated Mol wt or MW. Although widely used, the term is not technically correct; relative molecular mass is preferable.
very low birth weight (VLBW) see under infant.

avoirdupois weight

Etymology: OF, avoir de pois, to have weight
the English system of weights in which there are 7000 grains, 256 drams, or 16 ounces to 1 pound. One ounce in this system equals 28.35 g, and 1 pound equals 453.59 g. Compare apothecaries' weight. See also metric system.


The gravitational force exerted on an object, usually by the earth. The unit of weight is the newton (1 newton equals 0.225 lb). The difference between weight and mass is that the weight of an object varies with the force of gravity, but the mass remains the same. For example, an object weighs less on the moon than on earth because the force of gravity is less on the moon; but the mass of the object is the same in both places. See: mass (3)

Many diseases cause alterations of body weight (BW). BW decreases in Addison's disease, AIDS, cancer, chronic diarrhea, chronic infections, untreated type I diabetes mellitus, anorexia, prolonged lactation, marasmus, obstruction of the pylorus or thoracic duct, starvation, tuberculosis, and peptic ulcer.

Normal weight depends on the frame of the individual. See: table

apothecaries' weight

See: apothecaries' weights and measures

atomic weight

Abbreviation: at. wt.
The weight of an atom of an element compared with that of 112 the weight of carbon-12. The term is widely used, but the correct term is atomic mass.

avoirdupois weight

See: avoirdupois measure

birth weight

The weight of a newborn. The normal weight of a newborn is between 5.5 lb (2.5 kg) and 10 lb (4.5 kg) and is directly related to the gestational age at which the infant was born. Birth weight is an important index of maturation and chance for survival. Weight of less than 2.5 kg is known as low birth weight (LBW) and is associated with an increased chance of death in the perinatal period. Medical advances have increased the chance of survival of newborns of 2.0 kg or more. See: large for gestational age; small for gestational age See: low birth weight

dosing weight

The body weight used for calculating the appropriate dosage of a medication for those whose weight exceeds the usual average range. Weight-based dosing is used to correct for different drug distributions and pharmacodynamics in overweight or obese patients.


Obese patients metabolize fat-soluble medications differently from lean patients, and the differences may result in clinically important undermedication or overmedication. One formula used to calculate a safe weight-based dosage for obese patients depends on the total body weight (TBW) and ideal body weight (IBW) as follows: dosing weight = (0.3)(TBW–IBW) + IBW.

drained weight

The weight of food solids that remain after the liquids in which they have been prepared are removed.

dry weight

The body weight of a person after ideal hemodialysis, i.e., of a patient in renal failure who has neither edema nor high blood pressure.

equivalent weight

An obsolete term for the weight of a chemical element that is equivalent to and will replace a hydrogen atom (1.008 g) in a chemical reaction.

extremely low birth weight

Abbreviation: ELBW
A birth weight of less than 1000 g (2.2 lb).

gram molecular weight

Gram molecular mass.

ideal body weight

Abbreviation: IBW
The weight in pounds or kilograms a person should weigh, based on height and frame, to achieve and maintain optimal health. Several tables, such as the Metropolitan Life Height and Weight Table, show ideal body weights for men and women of varying heights. These references may be used to help set goals for patients who are underweight or overweight. See: weight for table

low birth weight

Abbreviation: LBW
Abnormally low weight of a newborn, usually less than 2500 g. Its causes include: preterm delivery of less than 37 weeks, multiple gestation, an abnormal uterus or cervix, congenital (genetic) anomalies in the fetus, maternal smoking or illicit drug use, placental malformation or malfunction, inadequate maternal nutrition, or a variety of other socioeconomic problems. Early, regular prenatal care and control of chronic and acute health problems help reduce risk. A series of ultrasounds can monitor fetal development. Early delivery is necessary if the fetus does not show signs of improvement. Incomplete maturation of the newborn's lungs is the most common cause of morbidity and mortality in LBW infants. Surfactants and a variety of neonatal technological supports decrease burden of this disease. Nursing/perinatal considerations include maintaining normal body temperature; diagnosis and treatment of hypoglycemia; maintenance of fluid, electrolyte, and nutritional status; and careful monitoring of newborn intake and output. Respiratory distress may be present, requiring oxygen and ventilation. Many preterm infants also have hyperbilirubinemia and are treated with phototherapy.

molecular weight

Abbreviation: mol. wt.; MW
The weight of a molecule attained by totaling the atomic weight (mass) of its constituent atoms.
See: atomic weight

set point weight

The concept that body weight is controlled by the central nervous system and set at a certain value. The value is more or less stable until something occurs to alter it, e.g., when a disturbance of hypothalamic function interferes with the satiety and feeding centers.

troy weight

A system of weighing gold, silver, precious metals, and jewels in which 5760 gr equal 1 lb (1gr equals 0.0648 g).

usual body weight

Abbreviation: UBW
Body weight value used to compare a person's current weight with his or her own baseline weight. The UBW may be a more realistic goal than the ideal body weight for some individuals. See: ideal body weight

very low birth weight

Abbreviation: VLBW
A body weight at delivery of less than 1500 g (but more than 500 g). Newborns that are this small make up about 1% of all births in the U.S. but account for about 60% of deaths in the first month of life.

weight in volume

Abbreviation: w/v
The amount by weight (mass) of a solid substance dissolved in a measured quantity of liquid. Percent w/v expresses the number of grams of an ingredient in 100 mL of solution.

weight in weight

Abbreviation: w/w
The amount by weight of a solid substance dissolved in a known amount (by weight) of liquid. Percent w/w expresses the number of grams of one ingredient in 100 g of solution.
SOURCE OF BASIC DATA: Build Study, 1979, Society of Actuaries and Association of Life Insurance Medical Directors of America, 1980. Copyright 1983 Metropolitan Life Insurance Company. Reprinted Courtesy of Metropolitan Life Insurance Company, Statistical Bulletin.Copyright 1983 Metropolitan Life Insurance Company.* Shoes with 1-in. heels.† Indoor clothing weighing 5 lb for men and 3 lb for women.
Height (in shoes)*Weight in Pounds (in indoor clothing)†Height (in shoes)*Weight in Pounds (in indoor clothing)†
Ft.In.Small FrameMedium FrameLarge FrameFt.In.Small FrameMedium FrameLarge Frame
5 2128–134131–141138–150410102–111109–121118–131
5 3130–136133–143140–153411103–113111–123120–134
5 4132–138135–145142–1565 0104–115113–126122–137
5 5134–140137–148144–1605 1106–118115–129125–140
5 6136–142139–151146–1645 2108–121118–132128–143
5 7138–145142–154149–1685 3111–124121–135131–147
5 8140–148145–157152–1725 4114–127124–138134–151
5 9142–151148–160155–1765 5117–130127–141137–155
510144–154151–163158–1805 6120–133130–144140–159
511146–157154–166161–1845 7123–136133–147143–163
6 0149–160157–170164–1885 8126–139136–150146–167
6 1152–164160–174168–1925 9129–142139–153149–170
6 2155–168164–178172–197510132–145142–156152–173
6 3158–172167–182176–202511135–148145–159155–176
6 4162–176171–187181–2076 0138–151148–162158–179


heaviness; the degree to which a body is drawn toward the earth by gravity. See also Tables 4.1 and 4.2.

apothecaries' weight
an outmoded system of weight used in compounding prescriptions based on the grain (equivalent 64.8 mg). Its units are the scruple (20 grains), dram (3 scruples), ounce (8 drams) and pound (12 ounces). See also Tables 4.2 and 4.3.
atomic weight
the weight of an atom of a chemical element, compared with the weight of an atom of carbon-12, which is taken as 12.00000.
avoirdupois weight
the system of weight still used for ordinary commodities in some English-speaking countries. Its units are the dram (27.344 grains), ounce (16 drams) and pound (16 ounces).
birth weight
weight of the newborn at the time of birth.
body weight
the animal's weight. In herbivores this is often debatable because of the variation in 'gut-fill' depending on the availability of palatable food. In the absence of scales the weights of large animals are often estimated on the basis of their age and their girth just behind the elbow. Called also liveweight. See also body condition score.
body weight-to-surface area
determination of many drug dosages is physiologically more accurate when based on body surface area rather than body weight; used particularly in cancer chemotherapy. For conversion table for use in dogs see Table 21.
equivalent weight
the weight in grams of a substance that is equivalent in a chemical reaction to 1.008 g of hydrogen. See also chemical equivalent.
weight gain
increase in body weight for specific periods; the principal measure of productivity in meat animals.
weight loss
the loss of body weight from that previously measured. This estimate must take into account the difference in 'gut-fill' and the effects of developing pregnancy and recent parturition.
metric weight
see Tables 4.1 and 4.2.
molecular weight
the weight of a molecule of a chemical compound as compared with the weight of an atom of carbon-12; it is equal to the sum of the weights of its constituent atoms. Abbreviated mol. wt. See also Table 6.
shifting weight limb to limb
sign indicative of lameness especially in horses; while standing the horse is continually shifting its weight from one limb to the opposite one of the pair.