# Comparisons of Measurement Systems

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# Comparisons of Measurement Systems

## Household Or U.S. Customary System

The household or U.S. customary system of measure is being introduced first because much of it is already familiar. From elementary school to the present, these measurements have been taught and used in your daily life, such as with cooking. Measurements are based on the English system of measures, which had its beginnings with the Greeks and Romans. These measurements will most likely be used in the home setting for administration of medications, although use of a measurement device that is provided with the medication increases patient safety. Therefore, you must be familiar with this system, although it is the least accurate of the measurement systems. In a hospital setting, these measurements would not be as appropriate.

Household measurements are expressed in Arabic numbers with the abbreviation for each following the number, such as 5 tsp or pt. Table 4-1 provides the basic household measurements for weight accompanied by abbreviations and equivalents as appropriate.

TABLE 4.1

Household Measurements of Weight

 MEASUREMENT UNIT ABBREVIATION EQUIVALENT Ounce oz — Pound lb, # 16 oz Ton T 2000#

Table 4-2 gives the measurements of length often seen in the medical setting. A mile is also a measurement of length but is not used in pharmaceutical calculations.

TABLE 4.2

Household Measurements of Length

 MEASUREMENT UNIT ABBREVIATION EQUIVALENTS Inch in, ″ — Foot ft, ′ 12 inches Yard yd 36 inches, 3 feet

Table 4-3 shows the household measurements of volume or liquid used most frequently in the home and in pharmaceutical calculations. Always remember that the size of a drop is totally dependent on the size of the opening in the dropper and viscosity of the liquid; therefore the 60 drops per teaspoon often found in measurement tables for household measurements is only an approximation. Drops used with intravenous therapy are stated in invariable amounts in the metric system as will be seen in later chapters. Also, household utensils are not necessarily accurate, so the amounts measured in these utensils should be considered only approximations.

TABLE 4.3

Household Measurements of Volume

 MEASUREMENT UNIT ABBREVIATION EQUIVALENTS Drops gtts — Teaspoon tsp, Tsp, t 60 drops (depending on the size of the dropper and the viscosity of the medication) Tablespoon tbsp, Tbsp, tbs, T 3 teaspoons Ounce oz 2 tbsp or 6 tsp Cup C, c 8 oz Pint pt 2 c, 16 oz Quart qt 2 pt, 4 c, 32 oz Gallon gal 4 qt, 8 pt, 16 c, 128 oz

### Using Ratio and Proportion for Finding Equivalency with Household System

Example 4-1

A known factor is 1 ft = 12 inches. Use ratio and proportion to calculate the number of inches in 4 feet.

Known Unknown

After cross multiplying the equation will be as follows:

< ?xml:namespace prefix = "mml" />1x=48 in NOTE: ft may be cancelled because both equivalents of the same measurement are known and appear on both sides of the fractional equation.

So,4 ft=48inches because thexis asking for inches. Example 4-2

4tbsp=_____tsp Known Unknown

3tsp:1tbsp::xtsp:4tbsp 1x=12 tsp NOTE: tbsp may be cancelled because both equivalents of the same measurement are known and appear on both sides of the fractional equation.

### Using Fractional Method for Finding Equivalency in Household Measurements

Another method of solving the unknown is to place the known equivalent and unknown equivalent into fractions and cross-multiply, as follows:

4 ft=_________in(Unknown equivalent)1 ft=12 in(Known equivalent) NOTE: ft may be cancelled because both equivalents of the same measurement are known on the functional equation.

x in=12×4or48 Therefore,4 ft=48 in OR

4 tbsp=___________tsp(Unknown equivalent)3 tsp=1 tbsp(Known equivalent) NOTE: tbsp may be cancelled because both equivalents of the same measurement are known.

xtsp=3×4=12tsp Therefore,4 tbsp=12 tsp. Example 4-3

To set up this problem, use a proportion as follows:

KnownUnknown1ft:12::2 ft:xinches x=24inches Now add ″ to the 24″ as indicated in the problem.

So the infant’s length is ″.

OR

Known Unknown

1×xin=2×12orx=24in 24inches+112inches=2512inches Example 4-4

KnownUnknown1tbsp:3 tsp::x:1 tsp 