# Estimating an Object’s Length

Learning how to estimate the length of an object without using measuring tools is a second grade, Common Core math skill: 2.MD.3. Below we show two videos that demonstrate this standard. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.

Prior Learnings

Your students will have learned how to measure objects through non-standard units, like using paperclips to measure a pencil (1.MD.1). They should also be able to compare objects using terms like longer, shorter, longest, and shortest (1.MD.2).

Future Learnings

In the future, understanding how to measure objects with a ruler will help your students expand on and apply the concept elsewhere. Students will be able to make a line plot, measure objects, and place those measurements on the plot (2.MD.9). Your students will also be able to use rulers marked with halves and fourths of an inch (3.MD.3) and apply “linear measurement to measure perimeter and area” (3.MD.5- 8).

Common Core Standard: 2.MD.3 - Estimate lengths using units of inches, feet, centimeters, and meters

Students who understand this principle can:

1. Without using a measurement tool, grasp mental and visual information to determine a measurement.
2. Justify why their estimate is reasonable.
3. Select the appropriate unit of measurement to estimate.

Video 1: Estimating Different Lengths

The video begins by explaining that people can measure things, both big and small. Then, different ways of measuring (without using measuring tools) are explained and depicted.

First, the video discusses the inch.

1. It is a small measurement, about as long as a quarter coin.
2. Imaging laying quarters along a crayon can help estimate its length.
3. The crayon is about 4 inches long.

Next, the video discusses the foot.

1. It is a bigger measurement and about the size of your foot.
2. If you walk along a couch, you can find how many feet long it is.
3. The couch is 8 feet long.

Next, the video discusses the meter.

1. It is about as long as taking a big step.
2. Someone in Kindergarten is 1 meter tall.
3. A big adult is 2 meters tall.

The last measurement is the centimeter.

2. It can be used to measure small objects.
3. The ladybug is 1 centimeter long.

Video 2: Which Measurement is Best?

This video offers 2 word problems about measurement for students to solve. It walks students through the reasoning and estimates the lengths of both a small and large item.

First, the video explains that students will be estimating lengths with customary units: inches, feet, and yards.

1. Inch = about the length of a paper clip.
2. Foot = about the length of a person’s foot.
3. Yard = about the length of a baseball bat.

The first question is, “Which customary unit of length would you use to measure a DVD case?”

Reasoning Points: 1) height of a DVD case is a small measurement; 2) feet or yards would be too big, so using inches is the best choice.

1. Students must estimate the length of the case.
a. 8 inches
b. 25 inches
c. 3 feet
2. Students can imagine the case next to a piece of paper which is about 11 inches.
3. So, students can guess the length of a DVD case is 8 inches.

The second question is, “Which customary unit of length would you use to measure a basketball hoop?”

Reasoning Points: 1) The height of a professional basketball hoop is too big to use inches; 2) the hoop is larger than a person, so using yards (the biggest unit) is the best choice.

1. Students can imagine how many baseball bats they can place along the hoop to answer the question:
a. 15 inches
b. 3 feet
c. 4 yards