1. 6
Measurement Systems and Their Equivalents

2. Knowledge and Accuracy
Healthcare professionals who deal with administration of medications must be:
Knowledgeable of weights and measures
Accurate in calculations
Careful in checking and verifying calculations

3. Units of Measure Pharmacology uses 3 systems of measurement:
Metric: most common, most accurate, and safest
Apothecary: older system
Household: less accurate

4. Metric System Based on decimals Gram (g): unit of weight
Liter (L): unit of volume
Meter (m): unit of length
Prefixes denote multiples or fractions of 10

5. Metric Prefixes (Latin)
0.1 or 1/10
deci- (d)
0.01 or 1/100
centi- (c)
0.001 or 1/1,000
milli- (m)
or 1/1,000,000
micro- (mc)
Value
Prefix

6. Metric Prefixes (Greek)
1,000,000
mega- (M)
1,000
kilo- (k)
100
hecto- (h) 10
deca- (da)
Value
Prefix

7. Metric System 1 cm = 10 mm Length 1 L = 1,000 mL Volume 1 kg = 1,000 g
1 mg = 1,000 mcg = g
1 g = 1,000 mg
Weight

8. Système International (SI)
Internationalized system of measurement based on gram for weight, liter for volume, and meter for length.
1 g = 1,000 mg = 1,000,000 mcg
1 L = 1,000 mL
1 m = 100 cm = 1,000 mm

9. Apothecary System Apothecary system measures volume in:
Minims (basic unit), drams (fluidrams), ounces, (fluidounces), pints (volume), quarts, gallons
Apothecary system measures weight in:
Grains (basic unit)

10. Apothecary System
Apothecary system is used for only a few drugs (acetaminophen, aspirin, and phenobarbital).

11. Apothecary Measurements
gallon (gal)
quart (qt) = pt ii
pint (pt) = qti = 0 32
pound (lb)
fluid ounce (℥) = pti = 16℥
ounce (oz or ℥)
fluiddram (fl dr)
dram (dr or ℨ)
Minim (♏)
grain (gr)
Volume
Weight

12. Household System
Household system used in most American homes but is not accurate.
Only household units used in measuring drugs are units of volume:
Drop
Tablespoon
Cup
Quart
Teaspoon
Ounce (fluid)
Pint
Gallon

13. Household Measurements
drop (gtt)
15 gtt = 1 mL
teaspoon (tsp)
1 tsp = 5 mL
tablespoon (T)
1 T = 3 tsp
ounce (oz)
1 oz = 2 T
cup
1 cup = 8 oz
pint (pt)
1 pt = 2 cups
quart (qt)
1 qt = 4 cups = 2 pt
gallon (gal)
1 gal = 4 qt

14. Milliequivalents
Milliequivalents (mEq): used to indicate strength of certain drugs
Defined as number of grams of equivalent weight of a drug contained in 1 mL of normal solution
Some drugs measured in mEq include potassium chloride, sodium bicarbonate, sodium chloride

15. Units and International Units
Units mainly measure potency of heparin, insulin, penicillin, and some vitamins.
International Units (IU) are used to measure vitamins.
Standardized by international agreement
Units and mEq cannot be directly converted into the metric, apothecary, or household systems.

16. Conversion Within and Between Measurement Systems
Drug doses are usually ordered in metric grams, milligrams, liters, and milliliters.
You must know how to convert between systems and within systems.

17. Approximate Volume Equivalents
2 pt = 1 qt
32 oz
960 mL
2 cups = 1 pt
16 oz
480 mL
8 oz = 1 cup
8 oz
240 mL
2 T = 1 oz
1 oz
30 mL
1 T
3–4 dr
15 mL
1 tsp
1 dr
5 mL
Household
Apothecary
Metric

18. Approximate Weight Equivalents
220 lb
1 kg
2.2 lb, gr xv, 15 gr
1 g (1,000 mg)
gr vii ss (7-1/2 gr)
0.5 g
gr i (1 gr)
60 mg
gr 1/2
30 mg
gr 1/4
15 mg
gr 1/60
1 mg
Apothecary
Metric

19. Temperature Conversion
Two common scales measure temperature: Celsius (C) and Fahrenheit (F).
Fahrenheit is used mostly in the U.S.; Celsius is used elsewhere.
Water freezes at 0°C, and at 32°F.
Water boils at 100°C and at 212°F.

20. Converting from Fahrenheit to Celsius
(°C x 1.8) + 32 = °F
(°F – 32) × 1.8 = °C OR
(°F – 32) × 5/9 = °C

21. Figure Thermometer showing the temperatures at which water freezes (0°C and 32°F) and boils (100°C and 212°F).