1. Systems of Measurement Metric / Apothecary / Household
Textbook Assignment:
Pickar, G. (2007). Dosage calculations: A ratio-proportion approach. (2nd ed.)
Chapter 3
Revised KBurger0808

2. The Metric System
The metric system is known for its simplicity. All units of measurement in the metric system are based on decimals—that is, units that increase or decrease by multiples of ten.
JCAHO recommends that the metric system by used exclusively for ordering, measuring, and reporting medications

3. Metrication of the World
The only countries not using SI Metric System are USA, Liberia and Myanmar

4. Metric Prefixes

5. International System (SI) of Metric Units and Abbreviations
Weight
Gram (base unit)-g
Milligram-mg
Microgram-mcg
Kilogram-kg

6. International System (SI) of Metric Units and Abbreviations
Volume
Liter (base unit)-L
Milliliter-mL
Cubic centimeter- cc *
* the cc abbreviation should not be used as it can be mis-interpreted
for zeroes if poorly written

7. International System (SI) of Metric Units and Abbreviations
Length
Meter (base unit)-m
Centimeter-cm
Millimeter-mm

8. Comparing Common Metric Units
PREFIX
KILO-
Hecto-
Deka-
BASE
DECI-
CENTI-
MILLI-
Decimilli-
Centimilli-
MICRO-
Weight
kilogram
gram
milligram
microgram
Volume
liter
deciliter
Milliliter
Length
meter
centimeter
Millimeter
Value to Base
1,000
100 10
1.0
0.1
0.01
0.001
0.0001

9. Rules of Metric Notation
Unit or abbreviation always follows amount
5 g NOT g 5
Decimals are used to designate fractional metric units
1.5 mL, NOT 1 mL

10. Rules of Metric Notation
Use a zero to emphasize decimal point for fractional metric units of less than 1
0.5 mg, NOT .5 mg
Will prevent potential dosage error
If you misinterpreted medication order as 5 mg instead of 0.5 mg
Dosage would be 10 times too much

11. Rules of Metric Notation
Omit unnecessary zeros
1.5 g, NOT 1.50 g
This is a critical rule
When in doubt, double-check
Ask writer for clarification

12. Most commonly used Metric Measurements and Equivalents
Weight
Unit
Abbreviation
Equivalents
gram g
1 g = 1,000 mg
milligram mg
1 mg = 1,000 mcg
microgram
mcg

13. Most Commonly Used Metric Measurements and Equivalents
Volume
Unit
Abbreviation
Equivalents
liter L
1 L = 1,000 mL
milliliter mL

14. The Apothecary System Originated in Greece
First system of medication measurement
One grain = weight of a single grain of wheat [60mg]
One grain = 60 mg is the ONLY apothecary conversion you will need to memorize

15. Apothecary System of Measurement
Currently being phased out as a system of measurement, but some units for dosage calculations that may still be seen are:
Grain (gr)
Ounce (oz)
!Notice the similarity between the abbreviation for
grain (gr) and gram (g). Be careful not to confuse them!
Other units in apothecary system not in use but still on some syringes and medicine cups are: minims and drams
Quantities are usually expressed in lowercase Roman numerals
Amounts greater than ten may be expressed in Arabic numbers
Except 15 (xv), 20 (xx), and 30 (xxx)

16. Apothecary System of Measurement
Quantities of less than one are expressed as fractions, except
One-half is expressed by the symbol ss
Abbreviation or symbol is clearly written before quantity Example: gr gr XV gr ½ gr ss

17. Apothecary System of Measurement
The apothecary system is NOT recommended for use by JCAHO.
Ask the prescriber to re-write in metric or if you are unsure about the exact meaning of any medical notation
Do not guess or assume
Ask writer for clarification

18. Household System of Measurement
Household measures are not accurate enough to be used in calculation of drug dosages.
However, when sending patients home with liquid medications, it is sometimes necessary.
Advise patients to use the measuring device provided with their prescription or an accurate measuring spoon [ not normal tableware]

19. Units uses in Household Measurement
Drop (gtt)
Teaspoon (t)
Tablespoon (T)
Ounce (oz)
Cup (cup)
Pint (pt)
Quart (qt)
Pound (lb)

20. Other Types of Drug Measurements Units
Standardized amount needed to produce a desired effect
Most commonly used for medications: Insulin, Heparin, Penicillin
CANNOT be abbreviated as (U) (See JCAHO Do Not Use List)
Must be written out as the word Units

21. Units

22. Milliequivalents (mEq)
One thousandth of an equivalent weight of a chemical
Most commonly used when referring to concentration of electrolytes

23. Milliequivalents (mEq)

24. Equivalents to MEMORIZE
1 grain (gr) = 60 milligrams (mg)
1 teaspoon (t) = 5 milliliters (mL)
1 tablespoon (T) = 3 teaspoons (t)
1 ounce (oz) = 30 milliliters (mL)
1 cup = 8 ounces (oz)
1 Kilogram (Kg) = 2.2 pounds (lbs)
1 liter (L) = 1000 milliliters (mL)
1 gram (g) = 1000 milligrams (mg)
1 milligram (mg) = 1000 micrograms (mcg)