DRUG CALCULATIONS
MAKING IT EASY

CLASS OUTLINE
 1)
review roman numerals
 2) review apothecary measurements
 3) review conversions
 4) review 3 steps to dosage
calculations
 5) practice, practice, practice

Plugging in to Memory
 Roman
Numerals
APOTHECARY MEASURES
 What
are we talking about?
CONVERSIONS
-
WITHIN SYSTEMS
BETWEEN DIFFERENT SYSTEMS
WITHIN SYSTEMS
 MEMORIZE:
1
gram (g or G) = 1000 milligrams (mg)
 1 liter (l or L) = 1000 milliliters (ml or
mL)
 3 teaspoons (t) = 1 tablespoon (T)
 1 cubic centimeter (cc) = 1 milliliter (ml)
BETWEEN SYSTEMS

MEMORIZE:
 1 gram (G, GM, gm) = 15 grains (gr)
 60 milligrams (mg) = 1 grain (gr)
 1 tablespoon (T) = 15 ml
 1 kilogram (kg) = 2.2 pounds (lb)
 1 ounce (oz) = 30 ml or 30 cc
 1 cc = 15 drops (gtt) or 15 minims (mx)
 1 inch (in) = 2.5 centimeters (cm)
STEPS TO CONVERSION
WITHIN SYSTEMS
 1)
Write down what you know in a ratio
or fraction format:
 Example:

1 Gram
1000 milligrams
 2)
Write down what you desire in a ratio
or fraction format to complete the
proportion:
 Example:

3 Grams
x milligrams
 Remember:
 The
numerator and denominator must
be the same unit of measurement
 The unknown value is referred to as “x”
The completed proportion:


1 Gram
1000 mg : :
 Cross
multiply
3 Grams
x milligrams
1
GM x X mg(s) = 3 GM x 1000 mg
 Drop the terms used for units of
measurement: 1 X = 3(1000)
 Solve for X: divide both sides of the
equation by the number preceding X:
 X = 3000
 1
1
X = 3000
BETWEEN SYSTEMS
 1)
Write down what you know in a
fraction format:


15 grains
1 gram
 2)
Complete the proportion by writing
down what you desire:


15 grains
1 gram : :
 HINT:
30 grains
X grams
Keep the units of measurements
in the correct spaces!

Drop the units of measurement
 Cross multiply

15 x X = 30 x 1
 15X = 30

Solve for X: Divide each side by the number
in front of X : X = 2
ANS: 2 Grams
VOILA!!
3 STEPS TO DOSAGE
CALCULATION:
 1)
Convert to units of same system and
similar unit
 2) STOP AND THINK
 3) Desired over amount on hand times
quantity
 EX:

desired
amount on hand x
quantity
SAMPLE PROBLEMS

1) Convert: 300 mg to grams

2) Convert: 120 mg to grains

3) Convert: 30 gr to grams

4) A child who weighs 55 pounds weighs ____
kilograms?

 5)
A patient is restricted to four 8ounce glasses of water per day. The
nurse knows that the patient’s fluid
intake is restricted to ____ mls per day.
 6)
The nurse administered aspirin gr v.
She knew this was equivalent to
_____milligrams(s).

7) Potassium chloride tablets are available in
300 mg doses. The physician prescribed gr
v. Give ____ tablet(s).

8) The physician prescribed Capoten, 1.5
grams daily in three equal doses, for
hypertension. The nurse would give _____
1000 mg tablet(s) three times a day.

9) Lasix 30 mg, IM, is prescribed as a
diuretic. Lasix was available as 40 mg/mL.
The nurse would give ______mL.

10) Scopolamine 0.3 mg was ordered
subcutaneously as a preanesthetic
medication. The medication was available in
ampules containing grains 1/200 per mL. The
nurse would give _____mL.

11) The physician prescribed 25 mg of
Librium, IM. Add 2 mL of diluent to yield 100
mg/2ML. The nurse should give _____ mL.

12) The physician prescribed 5 mg of
Garamycin for a child. The medication is
available as 20 mgs/mL. To give 5 mg, you
would give ____ mL.
PRACTICE, PRACTICE,
PRACTICE
 And
HOLLER if you need help!