Systems of Measurement

SYSTEMS OF
MEDICATION
MEASUREMENT
Jan Paolo M. Barandino, RN MAN

Clinical Instructor
System of Medication
Measurement
Apothecary Household Metric

APOTHECARY
• Originated in Greece
• FIRST System of measurement
• Currently phased out as a system of measurement,
but some units for dosage calculations may still be
seen as Grain (gr), Ounce (oz); syringes and
medicine cups: minims and drams
• Quantities are expressed in lowercase roman
numerals, amounts greater than TEN may be
expressed in arabic numbers
ONE GRAIN =
60 mg
ERROR ALERT!
• DO NOT confuse grains and grams.
• grains (gr)
• grams (g)
• DO NOT confuse symbols for drams and ounces.

• gram has extra line on top
APOTHECARY
• When writing a value in the apothecary system:
• If a value is less than 1, write it as a fraction.
• However, if the value is one half, write it as the
abbreviation “ss”
• Write the values with lowercase Roman
numerals
• Use the abbreviation gr to represent grain
• Write the abbreviation, symbol or unit before the
quantity.
• NOT recommended by JCAHO
LEARNING CHECKPOINT!
• Using the apothecary notation:
• Write four grains gr iv
• Write two and one-half grains gr iiss
• Write fifteen grains gr 15

METRIC SYSTEM
• Most logically organized/ widely used/ simple
• Conversion using multiplication and division
• Each basic unit of measurement is organized into
units of 10
• 10 mg x 10 = 100 mg
• 10 mg / 10 = 1 mg
• Basis units of measurement in the metric system
are:
• Meter (Length) Gram – g or gm
Liter – l or L
• Liter (Volume) Milligram – mg
• Gram (Weight) Milliliter - mL
METRIC SYSTEM
• Prefix before the basic unit indicates size
• KILO- multiply the basic unit by 1000
• Kilometer – 1000 meters
• Kilogram – 1000 grams
• Kiloliter – 1000 liters
PREFIX LENGTH VALUE
Kilo (k)- basic unit kilometer (km) 1 km = 1000 m
centi (c) centimeter (cm) 1 cm = 0.01 m
milli (m) millimeter (mm) 1 mm = 0.001 m
micro- (mc) micrometer (mcm) 1 mcm = 0.000001 m
METRIC SYSTEM
• Combining Prefixes and Units
LENGTH Weight Volume
PREFIX
(meter) (gram) (liter)
kilo (x 1000) kilometer (km) kilogram (kg) kiloliter (kL)
centi (÷ 100) centimeter (cm) centigram (cg) centiliter (cL)
milli (÷ 1000) millimeter (mm) milligram (mg) milliliter (mL)
micro (÷ micrometer (mcm) microgram (mcg) microliter (mcL)
1,000,000)
METRIC SYSTEM
• When writing a value in the metric system:
• Use Arabic numerals, with decimals to represent
any fractions
• 1.25 g to represent 1 1 /4 g
• 0.5 mg to represent ½ g
• 0.01 L to represent 1/100 L
• If the quantity is less than 1, include a 0 before
the decimal point. Delete any other zeros that
are not necessary.
• Do not write .750, instead write 0.75
• Do not write 5.0 instead 5
METRIC SYSTEM
• When writing a value in the metric system:
• Write the unit after the quantity with a space
between them
• 30 mg not mg 30
• Use lowercase letters for metric abbreviations.

However uppercase L to represent liter.
• Write mg, not MG
• Write mL, not ml
ERROR ALERT!
• Meter and gram are abbreviated with lowercase
letters.
• m
• gm
• Liter is abbreviated with an uppercase L, to

minimize the possibility of confusion between 1 and
the lowercase L
Which of the following is the correct
metric notation for six and two-eights
milliliter?
A. 6.28 mL
B. ml 6.25
C. 6 1/4mL
D. 6.25 mL
HOUSEHOLD MEASUREMENTS
• Most familiar to most people
• Include drops, teaspoons, tablespoons, and cups
for volume and pints and quarts for weight
• Advantage: familiarity and convenience
• Disadvantage: inaccuracy for some tools such as

teaspoons and cups, scales to measure pints or
quarts are not well calibrated
EQUIVALENTS OF MEASUREMENT
METRIC APOTHECARY HOUSEHOLD
1 mL 15-16 minims* 15 drops (gtt)
5 mL 1 dram* 1 teaspoon (tsp)
15 mL 4 drams* 1 tablespoon (tbsp)
30 mL 1 fluid ounce 2 tablespoons (tbsp)
240 mL 8 fluid ounces 1 cup (c)
480 mL (approx. 500 mL) 1 pint (pt) 1 pint (pt)
960 mL (approx. 1 L) 1 quart (qt) 1 quart (qt)
3,840 mL (approx. 4 L) 1 gallon (gal) 1 gallon (gal)
*Minims and drams are no longer acceptable units of measure for medication administration, although
medication cups and syringes still have them listed. Use mL for safe medication preparation. (Morris, 2014).
• Write six drops
6 gtts
• Write twelve ounces
12 oz
OTHER TYPES
• UNITS
• Standardized amount needed to produce a
desired effect
• Most commonly used for Insulin, Heparin
• Must be written out as the word UNIT/S
• MILLIEQUIVALENT (mEq)
• One thousandth of an equivalent weight of a
chemical
• Most commonly used when referring to
concentration of electrolytes (Sodium/
Potassium)
CLINICAL CALCULATIONS
• Conversion within ONE system
• Divide or multiply in the metric system
• Milligrams to grams, divide by 1000

• 1000 mg = 1 g
• 350 mg = 0.35 g
• Liters to milliliters, multiply by 1000

• 1 L = 1,000 mL
• 0.25 L = 250 mL
CLINICAL CALCULATIONS
• Conversion within ONE system
• Fluid Ounces to quarts, consult an equivalent

table
• 32 oz = 1 qt
• 8 oz = ¼ or 0.25 qt
7 mg = _____ mcg
A. 4500 mcg
B. 5000 mcg
C. 6000 mcg
D. 7000 mcg
0.87 mg= _____ mg
A. 870 mg
B. 875 mg
C. 750 mg
D. 700 mg
4 Tbsp = _____ mL
A. 40 mL
B. 50 mL
C. 55 mL
D. 60 mL
0.55 L = _____ mL
A. 0.550 mL
B. 550 mL
C. 55 mL
D. 555 mL
150 g = _____ kg
A. 0.15 kg
B. 1,500 kg
C. 150.5 kg
D. 1.50 kg
Dose Calculations
Ratio and
Formula Dimensional
Proportion
Method Analysis
Method
FORMULA METHOD
Dose ordered
X Amount on hand
Dose on hand
• Dose ordered is the amount of medication

prescribed
• Dose on hand is the dose of medication supplied
by the pharmacy
• Amount on hand is the basic unit or quantity of the
medication that contains the dose on hand
EXAMPLE 1
The health care provider orders morphine sulfate 2
mg IV. The medication is available in a vial
containing 10mg/ mL. Determine the amount to
administer.
Step 1: Estimate the answer.

Step 2: Set up the formula.
Step 3: Calculate the answer.
Step 4: Compare the answer in step 1 with the
answer in step 3.
0.2 mL
A patient is ordered 500 mg of Metformin
PO TID. Metformin is available in 250 mg
Tablets. How many tablets do you give to the
patient?

answer in step 3.
2 tablets
A patient is ordered 50 mg of Dilantin PO
BID. The unit only has the drug available in
125 mg/ 5 mL concentration. How much milliliters do
you give this patient per dose?

answer in step 3.
2 mL
A patient is ordered 50 mg of Dilantin PO
BID. The unit only has the drug available in
125 mg/ 10 mL concentration. How much milliliters do
you give this patient per dose?

answer in step 3.
4 mL
RATIO AND PROPORTION
1:2 = 4:8
• First and last numbers – extremes
• Second and third numbers - means
1:2 = 4:8
EXAMPLE 1
The health care provider orders 500 mg of Amoxicillin
to be administered in a gastric tube every 8 hours.
The bottle of Amoxicillin is labeled 400 mg/5 mL.
Calculate how much Amoxicillin should be
administered.

Step 2: Set up the formula. 6.25 mL
answer in step 3.
1 tablet : 500 mg = ___ tablet : 750 mg

answer in step 3.
1.5
If 125 mg of medication is in 2 capsules,
how many mg is in 10 capsules?

answer in step 3.
625 mg
If 90 mg of a medication is in 100 mL,
how many mL of solution contains 225 mg?

answer in step 3.
250 mL
REFERENCES
Fundamentals of Nursing 9th Edition by Potter and Perry
Calculation of Drug Dosages A Work text 10th edition by Sheila J. Ogden & Linda K
Fluharty
Clinical Nursing Calculations by Sienkiewicz & Almunen, 2017
McGraw Hill by Booth and Waley, 2010
Dosage Calculations: A Ratio-Proportion Approach, 2nd Edition, by Pickar G., 2007

Systems of Measurement

Uploaded by

Copyright:

Available Formats

Systems of Measurement

Uploaded by

Document Information

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Systems of Measurement

Uploaded by

Copyright:

Available Formats

SYSTEMS OF

Jan Paolo M. Barandino, RN MAN

Apothecary Household Metric

• DO NOT confuse symbols for drams and ounces.

• Write four grains gr iv

• Write two and one-half grains gr iiss

• Write fifteen grains gr 15

• Use lowercase letters for metric abbreviations.

• Liter is abbreviated with an uppercase L, to

• Advantage: familiarity and convenience

• Disadvantage: inaccuracy for some tools such as

• Write twelve ounces

• Milligrams to grams, divide by 1000

• Liters to milliliters, multiply by 1000

• Fluid Ounces to quarts, consult an equivalent

• Dose ordered is the amount of medication

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Step 1: Estimate the answer.

Clinical Nursing Calculations by Sienkiewicz & Almunen, 2017

McGraw Hill by Booth and Waley, 2010

Dosage Calculations: A Ratio-Proportion Approach, 2nd Edition, by Pickar G., 2007

You might also like