Math Background

Estimating and Measuring Amounts: Overview

Students explore the customary system of measurement in the first half of this chapter. This system of measurement is used most often in the United States. It includes linear measurement (length and distance), capacity (the amount that a container can hold), weight (how heavy an object is), and temperature (how hot or cold it is).

Students measured length using an inch (in.) ruler in Grade 2. See Measurement to review this skill.

Students will extend their knowledge this year by measuring to the nearest half inch. You can use the lesson Standard Units of Length: Developing the Concept, found within this Web site.

Students will also learn that feet (ft), yards (yd), and miles (mi) are used to measure length and distance. In third grade, focus students' attention on the appropriateness of each unit for measuring. For example, to measure the distance across the country, you use miles, not inches, feet, or yards. To measure the length of a playground, you use feet or yards, not inches or miles.

Refer to “When Students Ask” for some ideas you can use to introduce customary units of capacity and weight.

In the second half of the chapter, students explore the metric system of measurement. This system is used most often in other countries and it is the standard system of measurement for science. Use the first question in the “When Students Ask” section to introduce this topic. It will help students better understand why they are learning another system of measurement.

Just like the customary system, the metric system includes linear measurement (length and distance), capacity (the amount that a container can hold), mass (the amount of matter in an object), and temperature (how hot or cold it is).

The foundation of the metric system is the base-ten number system. Your students will discover this as they learn the different units of measurement and their equivalencies.

Metric Units of Length and Distance
10 centimeters (cm) = 1 decimeter (dm)
10 decimeters (dm) = 1 meter (m)
1,000 meters (m) = 1 kilometer (km)

Metric Units of Capacity
1,000 milliliters (mL) = 1 liter (L)

Metric Units of Mass
1,000 grams (g) = 1 kilogram (kg)

Refer to “When Students Ask” for ideas on how to introduce capacity and mass. As with the customary system of measurement, focus your students' attention on the appropriateness of each unit for measuring. For example, to measure the capacity of a fish tank, you use liters, not milliliters. To measure the mass of an elephant, you use kilograms, not grams.

Look at the bulletin board suggestion in “Tips and Tricks.” It will provide your students with daily practice in reading and recording temperature. You can use this activity when students are learning to measure temperature in degrees Fahrenheit (customary system) or degrees Celsius (metric system). As they learn about temperature, remind them that a thermometer is just like a number line that goes up and down instead of across. Although students have not been exposed to negative numbers, they will probably understand that the numbers below 0 on the thermometer are less than 0.

Remember that whether you are teaching the customary system or the metric system of measurement, hands-on activities are the best approach.


Houghton Mifflin Math Grade 3