1. Systems of Measurement
MAT 119
Chapter 3

2. Objectives
Interpret and properly express metric and household notation.
Recall metric and household equivalents.
Explain the use of milliequivalent (mEq), international unit, and unit, in dosage calculation

3. Systems
There are two systems used by health professionals: metric and household.
It is important to understand each system and how to convert from one system to another.
All prescriptions should be written with the metric system.

4. Systems continued
Three essential components of measurement associated with the prescription and administration within each system:
Weight
Volume
Length
NOTE: you can move from small to large & large to small in each system, but not between differing systems.

5. The Metric System
A decimal system, which means it is based on powers of 10.
The base units of the metric system:
Gram – weight
Liter – volume
Meter – length

6. Comparing Common Metric Units
Prefix
Kilo
Hecto
Deca
BASE
Deci
Centi
Milli
Deci-milli
Centi-milli
Micro
Weight
kilogram
Gram
Milli-gram
microgram
Volume
Liter
Milli-liter
Length
Meter
Centi-meter
Milli-meter
Value To
Base
1,000
100 10 1
0.1
0.01
0.001
0.0001 ∆
King
Henry
Died
From
drinking
chocolate
milk X X
X = mcg

7. Metric System Unit Abbreviation Equivalents Weight Gram g
1 g = 1000 mg = 1,000,000 mcg
Milligram mg
0.001 g = 1 mg = 1000 mcg
Microgram
mcg
g = mg = 1 mcg
Kilogram kg
1 kg = 1000 g
Volume
Liter L
1 L = 1000 mL
Milliliter mL
0.001 L = 1 mL
Length
Meter m
1 m = 100 cm = 1000 mm
Centimeter cm
0.01 m = 1 cm = 10 mm
Millimeter mm
0.001 m = 0.1 cm = 1 mm

8. The Apothecary System
While the Joint Commission recommends the metric system be used exclusively, rarely there are some apothecary notations still in use.
Notations are unusual and can cause confusion and ultimately a medication error.

9. Household System of Measurement
Some units used in household systems
ounce, pint, and quart
The unit of measure follows the amount
2 oz
25 t
375 T
5 c

10. Household System of Measurement
Unit
Abbreviation
Equivalents
drop
gtt
none
teaspoon
t (or tsp)
3 t = 1 T
tablespoon
T (or tbs)
1 T = 3 t
ounce (fluid)
ounce (weight)
fl oz oz
2 T = 1 fl oz
1 lb = 16 oz
cup
cup (may see c)
1 cup = 8 fl oz
pint pt
1 pt = 2 cups = 16 fl oz
quart qt
1 qt = 2 pt = 4 cups = 32 fl oz
pound lb

11. Other common drug measurements
Four (4) other measurements may be used to indicate quantity of medication prescribed:
International unit – unit of potency for vitamins and chemicals
Unit – standardized amount needed to produce a desired effect; penicillin, heparin, insulin
Milliunit – one thousandth of a unit; oxytocin
Milliequivalent (mEq) – unit used when referring to the concentration of serum electrolytes: calcium, magnesium, potassium, and sodium

12. Units

13. Milliequivalents (mEq)