Teaching Models

Customary Measurement

Measurement is the process of determining a number that represents a particular attribute of an object. This process begins by defining a unit object that has a measure of 1. Once a unit of measure is defined, measurement is the process of determining how many copies of this unit fit, without overlap, along a side of the given object. A number that specifies a quantity in terms of a unit of measurement is called a denominate number.

Suppose a line segment S is designated as a segment of unit length with a measure of 1. Then the length of another line segment T is determined by how many copies of S, or parts of S, fit alongside T without overlap. In the illustration below, S is the unit segment. Because two and one-half copies of S fit alongside T, T has a length of 21/2 units.

Line segments

The accuracy of a measurement depends upon the size of the unit of measure being used. The smaller the unit the more precise the measurement. For instance, a measurement rounded to the nearest half inch is more precise than a measurement rounded to the nearest inch.

Abbreviations are sometimes used in denominate numbers. These abbreviations generally do not have periods after them, except for “in.” (A period is used in the abbreviation for inch to avoid confusion with the word in.) These abbreviations are used for both singular and plural units of measure, so “ft” is the abbreviation for foot and feet and “m” is the abbreviation for meter and meters. Students need to memorize the abbreviations for measures studied in this chapter.

Customary System of Measurement
In the customary system of measurement used in the United States, the common units used to measure length include inch, foot, yard, and mile. Students should know the following equivalencies and abbreviations.

12 inches (in.) = 1 foot (ft)
3 feet (ft) = 1 yard (yd)
36 inches (in.) = 1 yard (yd)
5,280 feet (ft) = 1 mile (mi)
1,760 yards (yd) = 1 mile (mi)

In the customary system of measurement, the common unit of measures and abbreviations for capacity and weight are shown below. Students should know the following equivalencies and abbreviations.

2 cups (c) = 1 pint (pt)
2 pints (pt) = 1 quart (qt)
4 quarts (qt) = 1 gallon (gal)
16 ounces (oz) = 1 pound (lb)

Teaching Model 13.2: Measure to the Nearest Half Inch

Houghton Mifflin Math Grade 3