Metric Conversions, Roman
Numerals, and Fractions
1
Introduction
 The
ability to manipulate conversions is a
required competency of pharmacy
technicians
 It is a foundation for filling orders and
calculating dosages in the pharmacy
 All transcribing calculations need to be
checked by a pharmacist
2
Introduction (Continued)
 Pharmacy
measurements come from
different regions of the world
 The
four most common types of
calculation systems are:
 Metric
system
 Household measurements
 Apothecary system
 Avoirdupois system
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Introduction (Continued)
A
good way to become familiar with
common pharmacy measurements is
to start with what you know and then
slowly build on that knowledge
 The
pharmacy technician must translate
the doctor’s orders into lay terms
 You
must make the instructions easy
enough for a child to understand
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Metric System
 Used
throughout pharmacy because of
its accuracy
 Metric units include:
 Milliliters,
cubic centimeters,
and liters for volume
 Kilograms, grams, milligrams, and
micrograms for weight
 Millimeters and meters for distance
5
Metric System (Continued)
 There
is a 1000-unit difference between
each measurement
Most Common Metric Measurements
kg______g________mg________mcg
1000x
1000x
1000x
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Metric System (Continued)
 The
use of millimeters is reserved for
drug calculations based on body surface
areas
 Knowing the basics for volume and
weight conversions is adequate
7
Writing Units Using Each System
(Continued)
 Metric
measurements
cc and ml can be used interchangeably
 Dry weights use mcg, mg, g, and kg
 Liquid volumes use ml and L

8
Household Measurements
The most common measurement system still
used in the United States is the household
system
 Measurements come in a variety of units

Volume refers to liquids
 Weight refers to dry ingredients
 Length refers to distance
 Most common measurement is the teaspoon

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Common Household
Measurements
Household
Measurements
(Volume)
1 teaspoon
1 tablespoon
1 cup
1 pint
1 quart
1 gallon
Metric
(Volume)
5 ml or cc*
15 ml or cc
240 ml or cc
480 ml or cc
960 ml or cc
3840 ml or cc
or 3.84 L
Household
1 teaspoon
3 teaspoons
8 ounces
2 cups
4 cups
16 cups
*Remember that 1 ml and 1 cc contain the same amount of liquid.
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Apothecary System
 Originated
in Europe
 Units used in this system are grains and
scruples for dry weight
 Drams and minims for liquids
 More common measurements include
ounces and pounds
11
Writing Units Using Each System
(Continued)
 Apothecary
measurements
Dry weights use pounds, ounces, drams,
scruples, and grains
 Liquid volume weights use gallons, pints,
fluid ounces, fluid drams, and minims

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Apothecary Weights
Dry Weight
1 grain
15 grains
20 grains
1 dram
1 ounce
1 pound
=
=
=
=
=
=
=
=
=
=
=
=
=
60 mg
1 gram
Э1
Э3
8 or
Э 24
gr 480
31.1 grams
16 ounces
96
Э 288
gr 5760
454 grams
Fluid Weight
1 dram
8 drams
3 scruples*
= 60
= 480
=1
*Scruples and minims are not commonly used units
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Important Differences Among
Systems

The metric system is used for compounding
drugs

There are differences among manufacturer’s
products and their weights

Conversions with these variances are
approximate

A pint can be 473 ml, 480 ml, or 500 ml

1 pound = 454 g in metric, but only 373 g in
the apothecary system
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Conversion Table:
Apothecary/Metric/Household
Apothecary
Volume
Apothecary
Weight
Metric
Volume
Metric
Weight
Common
Household
1
1
30 ml
30 g
2 tbsp
4
4
15 ml
15 g
1 tbsp
2
2
7.5 ml
7.5 g
½ tbsp
1
gr 60
4 ml
4g
1 tsp
2 ml
2g
½ tsp
½
gr 30
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Oral cups show equivalent volumes
between household to metric and
household to apothecary.
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Avoirdupois System
 Originated
in England
 Similar to the apothecary system
because it also uses grains, ounces, and
pounds for weight
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Conversions
 Metric
system slide
 When
converting metric measurements
from one unit to another you need to move
the decimal either to the right or to the left
 All changes of the metric system involve
either dividing or multiplying by tens
 Each unit is a multiple of 1000
 Remember the difference between 1 kg, 1
g, 1 mg, and 1 mcg is 1000
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Conversions (Continued)

Method for determining metric conversions
Left
Largest
Right
Smallest
1________1_______1_________1
1 kg
1000 g
1,000,000 mg
1,000,000,000mcg
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Conversions (Continued)
 Decimals
are not placed at the end of a
number unless there is a fraction, such
as 1.1 kg
 Decimals and periods have been the
main source of mistakes in pharmacies
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Conversions (Continued)
 When
converting from large to small,
you multiply
 When
converting from small to large,
you divide
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Conversions (Continued)
 Fractions
 Percentage
is always a portion of 100
 To
convert a decimal into a percentage
you simply multiply by 100
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Determining Weight
Because
all manufacturers provide proper
dosing regimens based on kilograms, it is
necessary to convert pounds into kilograms
There
are 2.2 pounds per kilogram
16 ounces = 1 lb
2.2 pounds = 1 kg
To determine how many kg in 1 lb, divide
To determine how many lbs in 1 kg, multiply
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Roman Numerals
 The
number system commonly used in
the United States is the Arabic system,
consisting of numbers 1, 2, 3, and so
forth
 Many physicians use Roman numerals to
indicate the quantity of tablets or
capsules to be filled or to order the
strength of medication
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Roman Numerals (Continued)
 When
working with Roman numerals,
remember that if a larger number is
placed in front of a smaller one, you
must add both to determine the value
 However,
if a smaller number is placed
before a larger number, then you must
subtract
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Roman Numerals (Continued)
When a numeral is repeated, its value is
repeated.
 A numeral may not be repeated more than 3
times.
 V, L, & D are never repeated.
 When a smaller numeral is placed before a
larger numeral, it is subtracted from the
larger numeral: Ex: XC=100-10=90

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Roman Numerals cont’d
When a smaller numeral is placed after a
larger numeral, it is added to the larger
numeral. Ex: CL=100+50=150
 V, L, & D are never subtracted. Ex: LC is
incorrect.
 Never subtract more than one numeral.
 When subtracting, only use a numeral before
the next 2 higher-value numerals. Ex: use I
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before V & X, X before L & C

Roman Numeral Practice
 XIV
=
 XC =
 CIV =
 XL =
 VIII =
C =
 IV =
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Military Time
 In
hospital settings, international time,
also known as military time, is used
exclusively
 Orders are written 24 hours a day and
all medical-related caretakers must
understand exactly when the order was
written and when the medication or
treatment is to take place
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Military Time (Cont’d)




The system is based on 100
Starting with the first hour of the day, the clock
begins at 0100 (1 AM) through 2400 or 12
midnight
By using this system there is never any question
as to when an order was written or which order
came first
Never use a colon
Your Assignments




The room is separated in halves
Students on the side of the room by the windows will
create 15 practice exercises using Roman numbers
(and an answer key)
Students on the side of the room by the door will
create 15 practice exercises converting military time to
standard and standard to military (15 total exercises).
When finished, work all problems on the document
camera. Call on students using craft sticks or allow
them to work as a team
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