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Apothecary/metric equivalents


Exact equivalents

  • Selected abbreviations are listed below.
  • Other common abbreviations used in the medical field:
  • 1 fluid ounce = 30 milliliters
  • One liter of pure water weighs approximately one kilogram so 1cc (mL) of water weighs 1 gram.
  • "A spoonful" generally means heaped or rounded, with as much above the bowl of the spoon as in the spoon. However, a measure of liquid is a level spoonful.
  • 1 teaspoonful = 5 milliliters
  • 1 tablespoonful = 15 milliliters
  • 1 ounce = 30 grams
  • 1 gram = 15 grains
  • In 1866, the United Stated Congress legalized the use of the metric system within the United States. The law also established approximate equivalents between customary and metric measurements.
  • 1 gram = 1,000 milligrams
  • 1 milligram = 1,000 micrograms
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Exact equivalents
  • Note: Exact equivalents are used for compounding and calculations requiring a high degree of accuracy.
  • International units: An old measurement of vitamin activity determined by biological methods as opposed to new measures that are determined by direct chemical analysis.
  • An international unit is quantity of a biologic (such as a vitamin) that produces a particular biological effect agreed upon as an international standard. Many health foods and supplements still use i.u. (IU).
  • A grain is a unit of weight in the U.S. Customary System.
  • The apothecaries' system of mass is an obsolete system formerly used by apothecaries (now called pharmacists or chemists) in English-speaking countries. Sometimes "ap" is added to the front of the unit to identify it as part of the apothecaries' system.
  • During the first half of the 20th Century, the apothecaries' system was replaced by the metric system.
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Copyright © 2011 Natural Standard (

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The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.