1. The Apothecary & Household System of Measurement
Ms. Ryan
MCATC
Mecial Math

2. Apothecary System An old system of measurement
First used by apothecaries (early pharmacists) and moved from Europe to colonial America
Household system evolved from the apothecary system
Older medications are still measured in apothecary units

3. Apothecary System Terms
Dram – common unit of volume in the apothecary
Grain (gr) – basic unit
Minim – common unit of volume
Ounce – fluid ounces of volume
Unit (USP Unit) – amount of medication to produce an effect

4. Apothecary System The basic unit of weight is the grain (gr).
ERROR ALERT!
Do not confuse grains and grams.
grains (gr)
grams (g)
1 gr = 60 mg = 0.06 g

5. Apothecary System The three common units of volume are minim ( )
dram ( )
ounce ( )
ERROR ALERT!
Do not confuse the symbols for drams and ounces.
1 ounce ( ) = 8 drams ( )

6. Apothecary System Apothecary ounce is used in the United States.
8 ounces to a cup is commonly used in the home to measure liquids.
The dram is most frequently used to abbreviate teaspoonful which is nearly the same volume.

7. Apothecary Notation Rule
When writing a value in the apothecary system:
If a value is less than 1, write it as a fraction.
Unless the value is one-half, write it as the abbreviation ss.
Write the values with lowercase Roman numerals.
Write the abbreviation, symbol or unit before the quantity.

8. Examples for Practice gr iv or gr iv
1. Write four grains using apothecary notation.
gr iv or gr iv
2. Write two and one-half grains using apothecary notation.
gr iiss
Write twelve ounces using apothecary
notation.
xii

9. The Household Measurement System
Used in homes, particularly in kitchens, in the United States.
The units of household measure for volume include teaspoonful, tablespoonful, cup, pint, quart, and gallon.
The units of household measure for weight are pounds and ounces.
Measuring volume using the household measure is less accurate than using other systems because the measuring utensils can vary in size.
Nevertheless, household volume measure may be used in community pharmacy practice when dispensing drugs that will be administered in the patient’s home because patients may have other measuring devices at home.
Labels instructing patients on how to take a medication often use household measure units for this reason.

10. Apothecary and Household Equivalents
It is important to note that the fluid ounce is the same in household and in apothecary (pharmacy) volume measure.
However, the ounces used to signify weight are different.
There are 12 oz in an apothecary pound, while there are 16 oz in a household pound.
The household pound is the more commonly used equivalence.
Apothecary ounces = household ounces
Neither bases on multiples of 10

11. Abbreviations for Household Measures
Unit of Measurement
Abbreviations
drop
gt or gtt (plural)
teaspoon
tsp or t
tablespoon
tbsp or T
ounce
oz or

12. Abbreviations for Household Measures
Unit of Measurement
Abbreviation
cup c
pint pt
quart qt
gallon
gal

13. Examples for Practice
Write the quantity in Arabic numerals before the abbreviation for the unit.
Example: Write six drops using household notation.
6 gtt
Example: Write twelve ounces using household notation.
12 oz

14. Apothecary and Household Equivalent Measures
drop (gtt)
1 drop =
1 minim
teaspoon (tsp or t)
1 teaspoon
60 drops
tablespoon (T)
1 tablespoon
3 teaspoons
ounce (oz)
1 ounce
2 tablespoons
cup (c)
1 cup
8 ounces

15. Milliequivalents and Units
Milliequivalents (mEq)
The mEq is defined as of an equivalent weight of a chemical.
Sodium and potassium are often measured in mEq.
USP Units (U)
Medications such as insulin, heparin, and penicillin are measured in units (U).
Size of the Unit varies for each drug.

16. Converting Among Metric, Apothecary, and Household Systems
When calculating drug dosages, you must often convert among the metric, apothecary, and household systems.
You need to know how the measure of a quantity in one system compares to its measure in another system.
1 tsp = 5 mL = 5 cc