Medical Math
Operations and Formulas
Metric Abbreviations for Weight
Kilogram kg
Gram gm
Milligram mg
Microgram
mcg
Metric Equivalencies for
Weight
1 kilogram= 1000 g
1gram= 1000 mg
1 milligram= 1000 mcg
•
•
Household
1 cup
•
1 tablespoon
T (tbs)
•
1 teaspoon
t (tsp)
•
drop
gtt
•
pound
lb
Abbreviation /
C
Metric /
240 cc
Apothecary
15 cc or 15 ml
5 cc
depends on
size of the drop
2.2 lb = 1 kg
1 lb. = 16 oz
• The formula method:
D x Q =X
H
• D - dosage desired or ordered
H - what is on hand (available)
Q - unit of measure that
contains the available dose.
When using solid products
(tablets, capsules) Q is always 1
and can be eliminated. Q varies
when using liquid measures.
X - the unknown dosage you
need to administer
Units
• Calculating dosages in units (insulin,
heparin, pitocin, vitamins, some
antibiotics)
• Example: Ordered: Heparin 8000
units subcutaneous q12h
Available: Heparin 10,000 units
per ml
How much will you
administer?
•
Formula: 8000 units X 1 ml = 0.8 ml
10,000 units
Calculations based on body
weight
•
The first step is to convert the patient’s body
weight into kg. The formula is 2.2 lb. = 1 kg.
•
The second step is to calculate the medication
dose.
•
a. Calculate the daily dose
•
b. Divide the daily dose by the number of
doses to be administered.
•
c. Use either the ratio-proportion or formula
method to calculate the number of
tablets/capsules or volume to be
administered with each dose
Temperature Conversion
°C = (°F-32) 5/9 or 0.5556
°F = (°C) 9/5 or 1.8 + 32