MEDICATIONS AND CALCULATION
There are three systems of measurement used in measuring drugs and solutions. The three systems are household,
metric, and apothecary.
The apothecary method is outdated and will not be covered in this course. Words like drams, grains, and minims, are
associated with the apothecary method.
The household system is peculiar to the United States. Words like ounces, teaspoon, tablespoon and pounds are
associated with the household method.
The Metric system is the most widely used system of measurement. Words like gram, milligram (mg), liter, milliliter (ml)
and cubic centimeter (cc) are associated with the metric system.
The only countries NOT using the metric system of measurement are the United States and Myanmar (formerly Burma).
This course will cover household and metric systems of measurement.
METRIC SYSTEM
The metric system is a decimal system based on the power of 10. The basic units of measurement are:
Gram for weight
Liter for volume (liquids)
Meter for length
Prefixes used in the Metric System
Kilo=1,000=one thousand times
Centi=0.01 one hundredth part of
Milli=0.001=one thousandth part of
Micro=0.000001=one millionth part of
Measuring Weight in the Metric System
1 kilogram (kg.)=1000 grams (g.) (Remember, kilo means 1000 times)
1 gram (g.)=1000 milligrams (mg.) (remember milli means 1,000 part of)
1 milligram=1000 micrograms (mcg)
It is useful to memorize these equivalents so as to be able to calculate future medication problems.
While weight measurement is being introduced it is useful to memorize that there are 2.2 pounds (household) in one
kilogram. How much would you weigh in kgs?
There are many ways to calculate math problems. One of the most useful and broadly applicable methods is to use a
ratio and proportion. Let’s practice one here:
To figure out your weight in kilograms (kg) you would proceed as follows:
Place the known quantity on the left side of the ratio and the unknown side on the right:
2.2 lbs : 1 kg= 135 lbs (use your weight) : X kilograms
Before we proceed with solving the problem, note:
You must keep the formula consistent. The pounds are in the same place on both sides of the equation (left side), where
as the kilograms are on the right side of the equation.
In order to solve the problem we need to multiply “the means and the extremes”.
The means are the innermost part of the equation: 1 X 135 =135
The extremes are the outermost part of the equation: 2.2 x X = 2.2 X
We now must “solve for X “ : 135 = 2.2 X
In order to get X alone we must divide both sides of the equation by 2.2.
2.2 =1 X
2.2
135 = 61.4
2.2
, Therefore X = 61.4 kgs (One’s weight always sound better in kgs!)
The use of ratio and proportion is basic algebra. If you have forgotten this formula it is imperative to review and practice.
Solve some more weight problems using ratio and proportion. Try and figure out some of your family member’s weights
in kgs. We will be using this formula to solve many problems.
Some medications are ordered in mgs per kgs (mg/kg) or mcgs per kgs (mcg/kg), especially in pediatric and critical care
settings.
Measuring Volume in the Metric System
1 liter = 1000 milliliters (ml) or 1000 cubic centimeters (cc)
1 milliliter (ml)= 1 cubic centimeter. (mls and ccs are used interchangeably).
It is useful to memorize that there are 30 mls (metric) in one ounce (household).
The size of a standard coffee mug is 8 ounces. Let’s figure that out in mls using the ration and proportion method.
The known goes on the left (30 mls : 1 ounce)
The unknown on the right (X mls : 8 ounces)
This is how it looks as the ratio and proportion:
30 mls : 1 ounce = x mls : 8 ounces.
Multiply the means and the extremes:
1 X = 240
X=240 mls in an 8 ounce coffee mug
It is important to understand mls for many reasons. We deliver medication in metric volumes and calculate the patient ’s
intake and output in mls as well.
Solve some more metric conversions on your own. Many cans of food (tomato sauce, soups, cans of soda) have ounces
and mls volumes on the can. Set up the ratio and proportion yourself and see if your answer matches the one on the
can.
We will not be reviewing metric measurement of length in this course. It is used frequently in pediatrics to provide more
precise measurement of a child’s length and head circumference. It is also useful if you traveling and the signs are in
Kilometers!
Conversions Between Metric Units
There are shortcuts when converting within the metric system as the system is based on powers of 10 or 10ths.
When conversion is needed, first determine which measurement is larger and which is smaller.
Example: (kilogram; gram) (milligram; microgram) (liter; milliliter; cubic centimeter)
To convert a smaller unit to a larger one, divide by (1000) moving the decimal three places to the left:
300 mg= 0.300 g
180mcg=.180mg
3250ml=3.250 L
42g=0.042kg
(I always remember that there are 1000mg in a gram and 1000 mls in a liter in case I need to use ratio and proportion).
Converting Milliliters and Ounces
There is a shortcut to convert mls into ounces:
Divide the mls by 30:
240ml=8 ounces (take a look at a baby bottle)
60 ml=2 ounces
1000ml=33 ounces
(Even with the shortcut, remember there are 30 ml in 1 ounce)
There are three systems of measurement used in measuring drugs and solutions. The three systems are household,
metric, and apothecary.
The apothecary method is outdated and will not be covered in this course. Words like drams, grains, and minims, are
associated with the apothecary method.
The household system is peculiar to the United States. Words like ounces, teaspoon, tablespoon and pounds are
associated with the household method.
The Metric system is the most widely used system of measurement. Words like gram, milligram (mg), liter, milliliter (ml)
and cubic centimeter (cc) are associated with the metric system.
The only countries NOT using the metric system of measurement are the United States and Myanmar (formerly Burma).
This course will cover household and metric systems of measurement.
METRIC SYSTEM
The metric system is a decimal system based on the power of 10. The basic units of measurement are:
Gram for weight
Liter for volume (liquids)
Meter for length
Prefixes used in the Metric System
Kilo=1,000=one thousand times
Centi=0.01 one hundredth part of
Milli=0.001=one thousandth part of
Micro=0.000001=one millionth part of
Measuring Weight in the Metric System
1 kilogram (kg.)=1000 grams (g.) (Remember, kilo means 1000 times)
1 gram (g.)=1000 milligrams (mg.) (remember milli means 1,000 part of)
1 milligram=1000 micrograms (mcg)
It is useful to memorize these equivalents so as to be able to calculate future medication problems.
While weight measurement is being introduced it is useful to memorize that there are 2.2 pounds (household) in one
kilogram. How much would you weigh in kgs?
There are many ways to calculate math problems. One of the most useful and broadly applicable methods is to use a
ratio and proportion. Let’s practice one here:
To figure out your weight in kilograms (kg) you would proceed as follows:
Place the known quantity on the left side of the ratio and the unknown side on the right:
2.2 lbs : 1 kg= 135 lbs (use your weight) : X kilograms
Before we proceed with solving the problem, note:
You must keep the formula consistent. The pounds are in the same place on both sides of the equation (left side), where
as the kilograms are on the right side of the equation.
In order to solve the problem we need to multiply “the means and the extremes”.
The means are the innermost part of the equation: 1 X 135 =135
The extremes are the outermost part of the equation: 2.2 x X = 2.2 X
We now must “solve for X “ : 135 = 2.2 X
In order to get X alone we must divide both sides of the equation by 2.2.
2.2 =1 X
2.2
135 = 61.4
2.2
, Therefore X = 61.4 kgs (One’s weight always sound better in kgs!)
The use of ratio and proportion is basic algebra. If you have forgotten this formula it is imperative to review and practice.
Solve some more weight problems using ratio and proportion. Try and figure out some of your family member’s weights
in kgs. We will be using this formula to solve many problems.
Some medications are ordered in mgs per kgs (mg/kg) or mcgs per kgs (mcg/kg), especially in pediatric and critical care
settings.
Measuring Volume in the Metric System
1 liter = 1000 milliliters (ml) or 1000 cubic centimeters (cc)
1 milliliter (ml)= 1 cubic centimeter. (mls and ccs are used interchangeably).
It is useful to memorize that there are 30 mls (metric) in one ounce (household).
The size of a standard coffee mug is 8 ounces. Let’s figure that out in mls using the ration and proportion method.
The known goes on the left (30 mls : 1 ounce)
The unknown on the right (X mls : 8 ounces)
This is how it looks as the ratio and proportion:
30 mls : 1 ounce = x mls : 8 ounces.
Multiply the means and the extremes:
1 X = 240
X=240 mls in an 8 ounce coffee mug
It is important to understand mls for many reasons. We deliver medication in metric volumes and calculate the patient ’s
intake and output in mls as well.
Solve some more metric conversions on your own. Many cans of food (tomato sauce, soups, cans of soda) have ounces
and mls volumes on the can. Set up the ratio and proportion yourself and see if your answer matches the one on the
can.
We will not be reviewing metric measurement of length in this course. It is used frequently in pediatrics to provide more
precise measurement of a child’s length and head circumference. It is also useful if you traveling and the signs are in
Kilometers!
Conversions Between Metric Units
There are shortcuts when converting within the metric system as the system is based on powers of 10 or 10ths.
When conversion is needed, first determine which measurement is larger and which is smaller.
Example: (kilogram; gram) (milligram; microgram) (liter; milliliter; cubic centimeter)
To convert a smaller unit to a larger one, divide by (1000) moving the decimal three places to the left:
300 mg= 0.300 g
180mcg=.180mg
3250ml=3.250 L
42g=0.042kg
(I always remember that there are 1000mg in a gram and 1000 mls in a liter in case I need to use ratio and proportion).
Converting Milliliters and Ounces
There is a shortcut to convert mls into ounces:
Divide the mls by 30:
240ml=8 ounces (take a look at a baby bottle)
60 ml=2 ounces
1000ml=33 ounces
(Even with the shortcut, remember there are 30 ml in 1 ounce)
