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Units of Measure

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Pharmaceutical calculations involve four different systems of measure: the International System of Units (SI), formerly known as the metric system, apothecaries', avoirdupois', and household. SI is an international decimalized system of measurement that uses the following units: gram, liter, and meter. SI is a decimal system, in the sense that all multiples and submultiples of the base units are factors of powers of ten of the unit. Examples of the SI system include:

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  • Mega: 106
  • Kilo = 103
  • Deci = 10−1
  • Centi = 10−2
  • Milli = 10−3
  • Micro = 10−6
  • Nano = 10−9
  • Pico = 10−12

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The apothecaries' system is a traditional system of measurement using drams (liquids) and grains (solids) and is occasionally found in prescriptions. For example, a prescribed medicine being sold in four ounce (iv) bottles or five grains (V gr.) of aspirin. The system consists of two basic units, grains for solids and minims for liquids. Examples of the apothecaries' system are listed in Table 70-1.

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TABLE 70-1 Apothecaries' System of Measurea
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Table Graphic Jump Location
TABLE 70-2 Avoirdupois System of Measurea

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