Math Background

Estimating and Measuring Amounts: When Students Ask

  • Why do I need to learn about both customary units and metric units of measurement?
    Have students identify real-life situations in which they used customary units of measurement. Then have them identify real-life situations in which they used metric units of measurement. Although some students may only come up with situations for customary units, the experiences their classmates have had using metric units may help them better understand why they are learning both systems. Also, point out to students that in most countries metric units of measurement are used most often.
  • What is capacity and how do I measure it?
    Explain to students that capacity is the amount that a container can hold. Have students draw upon their own experiences with cooking and shopping to name some of the units of capacity they are familiar with. The customary units of capacity they will learn this year are pint (pt), cup (c), quart (qt), and gallon (gal). Give students the opportunity to investigate these units using pint, cup, quart, and gallon containers. For example, have them estimate and then measure the number of cups in one pint, pints in one quart, and quarts in one gallon.

    2 cups (c) =1 pint (pt)
    2 pints (pt) = 1 quart (qt)
    4 quarts (qt) = 1 gallon (gal)

    You can also have students use different-size containers such as a milk carton, water bottle, spoon, or eyedropper to estimate which container holds less than, more than, or about 1 customary unit. For example, a water bottle holds more than 1 pint. A spoon holds less than 1 cup. This activity can be adapted to metric units of capacity: milliliters (mL) and liters (L). A milk bottle holds about 1 liter. An eyedropper holds about 1 milliliter.

  • What is mass?
    Explain to students that mass is the amount of matter in an object. The metric units of mass are gram (g) and kilogram (kg). Have students explore the mass of different objects using a scale. Identify one object that has a mass of about 1 kilogram. Have students pick up other objects and estimate which objects have a mass that is less than, more than, or about 1 kilogram. Then have students use a scale to find the actual mass of each object. This activity is easily adaptable to customary units of weight: pound (lb) and ounces (oz). Lead students to discover that large objects may have a small mass or weight and small objects may have a great mass or weight.
  • Why are there so many different units of measurement?
    Students will discover the answer to this question when you respond with questions such as this: If feet and yards did not exist, how would we measure the height of our school? If the only unit of capacity was milliliters, what would it be like to measure the amount of water in a bathtub?

Houghton Mifflin Math Grade 3