The Metric System
The metric system is the official system of weights
and measures used by Navy Pharmacy Departments
for weighing and calculating pharmaceutical
The metric system is becoming the
accepted system throughout the world.
Corpsmen need to be concerned primarily with the
divisions of weight, volume, and linear measurement
of the metric system. Each of these divisions has a
primary or basic unit and is listed below:
Basic unit of weight is the gram, abbreviated g
Basic unit of volume is the liter, abbreviated l
Basic linear unit is the meter, abbreviated m
By using the prefixes deka, hecto, and kilo for
multiples of, respectively, ten, one hundred, and one
thousand basic units, and the prefixes micro, milli,
centi, and deci for one-ten thousandth, one- thousandth,
one-hundredth, and one-tenth, respectively, you have
the basic structure of the metric system. By applying the
appropriate basic unit to the scale of figure 6-1, you can
readily determine its proper terms. For example, using
the gram as the basic unit of weight, we can readily see
that 10 g equals 1 dekagram, 100 g equals 1 hectogram,
and 1000 g is referred to as a kilogram. Conversely,
going down the scale, 0.1 g is referred to as a decigram,
0.01 g is called a centigram, and 0.001 g is a milligram.
The Apothecary System
Although fast becoming obsolete, the apothecary
system for weighing and calculating pharmaceutical
preparations is still used and must be taken into
consideration. It has two divisions of measurement:
weight and volume. In this system, the basic unit of
weight is the grain (abbreviated gr), and the basic
unit of volume is the minim (abbreviated m).
The Avoirdupois System
The avoirdupois system is a system used in the
United States for ordinary commodities. The basic units
of the avoirdupois system are dram (27.344 grains),
ounce (16 drams), and pound (16 ounces).
Table of Weights and Measures
See table 6-1, a table of weights and measures;
study it thoroughly.
Converting Weights and Measures
Occasionally, there are times when it will be
necessary to convert weights and measures from one
system to another, either metric to apothecary or vice
versa. Since patients can hardly be expected to be
familiar with either system, always translate the
dosage directions on the prescription into a household
equivalent that they can understand.
measurements are standardized, on the assumption
that the utensils are common enough to be found in any
home. Table 6-2 is a table of household measures, with
their metric and apothecary equivalents.
For the conversion of specific
quantities in a prescription or in converting a
pharmaceutical formula from one system to
another, exact equivalents must be used.
As stated earlier, in the practice of pharmacy it may
be necessary to convert from one system to another to
dispense in their proper amounts the substances that
have been ordered. Although the denominations of the
metric system are not the same as the common
systems, the Bureau of International Standards has
established conversion standards that will satisfy the
degree of accuracy required in almost any practical
Ordinary pharmaceutical procedures
generally require something between two- and
three-figure accuracy, and the following tables of
conversion (tables 6-3 and 6-4) are more than
sufficient for practical use. Naturally, if potent agents
are involved, you must use a more precise conversion
factor for purposes of calculation.
Figure 6-1.Graph comparing the metric system with the