Units of Measure
Math for Clinical Practice
Weight
•
•
•
•
Kilogram = kg
Gram = g
Milligram = mg
Microgram = mcg
Length
• 1 meter = m
• Centimeter = cm
• Millimeter = mm
Volume
• 1 liter = L
• 1 milliliter = mL or cc
(cc is not to be used anymore according to
JACOH standards but it is a common error
since it has been used for years)
CC = mL
Length
• 1 meter (m) = 100 cm or 1000 mm
• Centimeter (cm) = 10 mm
• Millimeter (mm) = 0.1 cm
Household Abbreviations
• 1 ounce or oz
• Tablespoon = Tbs
• Teaspoon = tsp or t
Conversion of Metric Units
Household Measurement
• 1 ounce (oz) = 30 mL
• 1 tablespoon (Tbs) = 15 mL
• 1 teaspoon (tsp) = 5 mL
Ounces to mL
• You are doing intake and output and the
mother states the infant has consumed 3
½ ounces of formula. How many mL has
the infant consumed?
• 3.5 x 30 mL = 105 mL
• You would record 105 mL on the intake
record
Measuring Liquids
Tablespoons
• You are teaching a geriatric patient how to
measure her medications. She is to take
15 mL of liquid Maalox to aid digestion.
• You would instruct her to use what
household measuring device to take her
mediation?
• Teaspoon or tablespoon
• She would take one tablespoon of
medication.
Teaspoon
• You are working with a mother of a toddler
and she has been instructed to give the
child 1 ½ teaspoons of medication. You
are demonstrating how to give the
medication with a syringe with
measurements in mL.
• How many mL would you have her give?
1 Teaspoon = 5 ml
• 1 ½ teaspoons = 1.5 teaspoons
• 1.5 teaspoon x 5 mL = 7.5 mL
• You would have her draw up 7.5 mL in a
po syringe.
Nursing Alert
• Remember if there is not a number to the
left of the decimal point a zero is placed
there to highlight the decimal point
placement.
• Correct: 0.5 mL or 0.25 g
• Incorrect: 5.0 mL or 25.0 g
Nursing Alert
• Decide whether you are converting from
smaller unit to larger unit or larger unit to
smaller unit.
Liter to milliliters
• 1 liter (L) = 1000 milliliters (mL)
• 1.2 L = ___________
• 1.2 x 1000 = 1200 mL
Milliliters (mL) to Liters (L)
• Change mL to Liter (L)
• mL is smaller than a liter
• Move decimal point three places to the
right
• 750 mL = 0.75 L
Metric Units Weight
•
•
•
•
Kilogram = kg
1 kg = 1000 grams (g)
1 gram (g) = 1000 milligrams (mg)
1 milligram (mg) = 1000 micrograms mcg
How to calculate kilograms
• Remember you will weigh less in
kilograms
• To convert pounds to kilogram you divide
by 2.2
• Convert 100 pounds to kg
• 100 / 2.2 = 45.454 or 45.45
• In the infant / small child carry out to the
100th or two decimal places.
Example
• Convert the following metric
measurement:
• 0.2 mg = ______ g.
• (gram is larger than a mg)
• Need to move the decimal 3 places or
divide by 1000.
• Answer 0.2 mg = 0.0002 g
Example
• 100 mcg = ______ mg
• You are going from a smaller unit to a
larger unit.
• You would move the decimal point 3
places or divide by 1000.
• 100 mcg = 0.1 mg
International and
Milliequivalent Measures
International Units
• Heparin, insulin, penicillin, epoetin
products (Epogen, Procrit) are measured
in international units.
• Example: regular insulin 10 units SQ in am
• Example: penicillin 600,000 units IM x one
dose
Milliequivalent Measures
• Do not confuse with milligrams.
• Notation is mEq
• Milliequivalent measures the number of
grams of equivalent weight of a drug
contained in 1 mL of normal saline.
mEq
• Common drugs: sodium bicarbonate,
sodium chloride, potassium chloride.
• Examples:
• 10 mEq of potassium chloride to ½ L of IV
solution
• 15 mEq of sodium chloride to 1 L of IV
solution
Conversions
Conversions
• Clinical connection: often you need to
calculate between different systems of
measure.
Metric System
•
•
•
•
•
Metric System
1 kg = 1000 g
1 g = 1000 mg
1 mg = 1000 mcg
1 L = 1000 mL
Grains
60 mg = 1 gr
45 mg = ¾ gr
30 mg = ½ gr
15 mg = ¼ gr
10 mg = 1/6 gr
Conversion to Metric Equivalents
60 mg
gr1
45 mg
gr 1/4
Gr 3/4
gr 1/2
30 mg
15 mg
Practice Problems
•
•
•
•
•
•
•
gr ¾ = ___________ mg
gr ¼ = ___________ mg
gr 15 = ___________ mg
300 mg = _________ gr
60 mg = __________ gr
30 mg = __________ gr
gr 1/6 = ___________ mg
Practice problems
• The bottle of Tylenol states that you are to
give X (ten grains) of Tylenol.
• How many mgs are you giving ________
Chapter Review
Calculations in the Clinical
Setting
Ratio – Proportion Method
• Using the ratio proportion method offers a
systematic approach to solving clinical
math calculations.
The Set-up
• Solving the unknown
• The cookies and the eggs
• If the recipe states you need 2 eggs to
make 2 dozen cookies. How many eggs
do you need to make a dozen cookies?
• 24 cookies 12 cookies
• 2 eggs
= x eggs
Practice Problem
• Page 106
• Lorazepram 3 mg IV every 6 hours as
needed.
• Lorazepam is supplied as 4 mg / mL
The set-up
•
•
•
•
4 mg 3 mg
1mL = x mL
(cross multiply)
3 / 4 x = 0.75 mL
• You would draw up 0.75 mL to equal 2 mg
of Lorazepam
Practice Problem
• Page 108
• Phenytoin sodium 300 mg by mouth at
bedtime.
• Phenytoin sodium supplied as 125 mg / 5
mL.
The Set-up
• 125 mg
5 mL =
300 mg
x mL
(Cross multiple) (X is on the bottom)
1500
125 X = 12 mL equals 300 mg of the drug
Practice Problems
• Remember to label properly and put the x
on the bottom.
Body Weight
Review
• Pounds to kilograms
• Pounds divided by 2.3
• Practice problems 1-10 page 140-41
Practice Problem
• Neupogen 5 mcg/kg/day IV over 30
minutes.
• Patient weight = 174
Change Pounds to Kilograms
• 174 / 2.2 = 79.09 kg
Determine the dosage
• 5 mcg / kg / day
• 5 mcg x 79.09 (weight in kg) = 395.45 mcg
per dose
• Drug is rounded to 395 mcg per dose to
be added to 50 mL of Dextrose 5% in
Water.
Practice Problem
• Phenobarbital 30 – 120 mg / kg per day in
3 divided doses
• Physician orders the maximum dose or
120 mg / day to be given q 8 hours.
• 1st you would need to divide 120 mg by 3
doses = 40 mg per dose
Determine the Amount
• Phenobarbital is provided as 65 mg / mL
• For one dose you would need to draw up
how much of the medication?
• 40 mg = 60 mg
x mL
1 mL
40 mg = 0.66 mL
60 x