Chapter 2 – Metric, Apothecary, and Household Systems of
Measurement
Medicine cups: marked in metric units/apothecary units/household
measures
Metric System
Solids
Kilogram kg - body weight
Grams g gm - body weight (infants, premature babies)
Milligram mg - pharmaceuticals
Microgram mcg (μg) – pharmaceuticals (chemotherapy, hormones)
1 kg = 1000 g = 103
1 g = 1000 mg = 1, 000, 000 mcg = 106 mcg
1 mg = 1000 mcg
1 mcg = 0.001 mg = 0.000001 g
Use conversion factors
10 mg x (1g ) = 0.01 g
(1000mg)
2500 g x (1kg) = 2.5 kg
1000 g
GRAMS TO MILLIGRAMS
Decimal point is the anchor!
To multiply by 1000, move the decimal point three places to the right
Order: 0.25 g
Supply: tablets labeled 125 mg
Convert 0.25 g into mg
0.25 g x 1000mg/g = 250 mg
Mg Rules
1. write the order first
2. write the equivalent measure needed
3. use an arrow to show which way decimal place should move
4. open part of the arrow always faces larger measure
5. in equivalent 1 g = 1000 mg, the gram is larger measure.
(1000 mg makes up 1 g)
Order: 1.5 g
Supply: 500 mg
Convert g to mg
1.5 g > ______ mg
Note: changing an inequality into an equality
1.5 g = 1500 mg
MILLIGRAMS TO GRAMS
To divide by 1000, move the decimal point three places to the
left
Order: 15 mg
Supply 0.03 g
15. mg < g
15 mg = 0.015 g
Order: 500 mg
Supply: 1 g
500 mg < g inequality
500. mg = 0.5 g equality
Self test 2 - #9
Order: 5 mg
Supply: 1 g
5 mg < g inequality
5.mg = 0.005 g equality
GRAMS TO MILLIGRAMS: MOVE THREE PLACES TO RIGHT
MILLIGRAMS TO GRAMS: MOVE THREE PLACES TO LEFT
Changing Milligrams to Micrograms
1 mg = 1000 mcg
Multiply by 1000, move decimal place 3 places to the right
Example 1
Order: 0.1 mg
Supply: 200 mcg
0.1 mg > ____ mcg inequality
0.1 mg = 100 mcg equality
Convert 0.08 mg to mcg
0.08 mg > ____ mcg
0.080 mg = 80 mcg
Changing Micrograms to Milligrams
1 mg = 1000 mcg
Divide by 1000, move decimal place 3 places to the left
250 mcg = __?__ mg
250 mcg < mg
250 mcg = 0.250 mg
Apothecary System
Check symbols
http://www.lib.umich.edu/tcp/docs/dox/medical.html
http://www.mapharm.com/prescr_parts.htm
Dram – liquid measure
3i = 4 mL
Ounce – liquid measure
gtt - liquid measure drop
(guttae)
m – liquid measure minim
1 dram = 4 mL
1 ounce = 32 mL
1 drop = 1 minim
1 m = 1 gtt
Grain gr – solid measure
ṡṡ one-half
i one
i ṡṡ one and a half
ii
iii
iv 4
v
vi
6
vii
viii
ix
9
x
xi eleven
xii twelve
xiii thirteen
xiv fourteen
xv fifteen gr xv = 15 grains
gr x = 0.6 g = 600 mg or 650 mg
gr v = 0.3 g = 300 mg or 325 mg
gr i = 0.06 g = 60 mg or 65 mg
15 grains = 1000 mg; 1 grain = 60 mg
Check the manufacturer’s label
Household Measures
Teaspoon tsp (t)
Tablespoon tbsp (T)
Ounce oz (fl oz)
cup c
Pint pt
Quart qt
Pound lb
Gallon gal
2 c = 1 pt
2 pt = 1 qt
4 qt = 1 gal
16 oz = 1 lb
Household equivalents
1 tsp = 5 mL
3 tbsp = 15 mL
1 oz = 30 mL
1 pt = 500 mL = 0.5 L
1 qt ≈ 1 L = 1000 mL
2.2 lb = 1 kg
Metric Liquid Measures
Liter L
Milliliter mL (ml)
Cubic centimeter cc
1 mL = 1 cc
1L = 1000 mL
Liquid Apothecary Measures
Minim m
Dram dr
Ounce oz
Drop gtt
1 m = 1 gtt 1 minim = 1 drop
1 dr = 4 mL 1 dram = 4 mL
8 dr = 1 oz 8 drams = 1 ounce
Conversions among liquid measures
5 mL = 1 tsp
15 mL = 1 tbsp = ½ fl oz = 4 drams
30 mL = 2 tbsp = 1 fl oz = 8 drams
500 mL = 1 pt
1000 mL = 1 L = 1 qt = 2 pt
3 mL syringe Note: 1 mL = 16 minims
Length
Metric
Meter
1m = 100 cm
1 cm = 0.01 m
1000 mm = 1 m
0.001m = 1 mm
English
1 yard = 3 feet
1 foot = 12 inches
1 inch = 2.54 cm
Temperature Conversion
F = 9/5 C + 32
C = 5/9(F-32)