Measuring length, number lines, and graphs (grade 2) · lesson

Pick the right tool

💡 Use a ruler for short things and a tape or yardstick for long things.

A ruler is good for a pencil or a book.

A tape measure is good for a room. A clock measures time, not length.

🧠 How to think about it

Ask what you are measuring and how long it is. Then pick the tool that fits.

ruler: a strip with inches or centimeters
yardstick: a stick one yard long

🏡 Try it at home

Measure a spoon with a ruler. Measure a bed with a tape measure.

Small units, big numbers

💡 The smaller the unit, the more of them it takes, so the number gets bigger.

A rug is 3 feet long. In inches it is 36 inches.

Inches are small, so you need more of them.

🧠 How to think about it

Centimeters are the smallest unit here. A desk measured in centimeters gets the biggest number.

unit: the size you measure with
centimeter: a very small unit, about a finger wide

🏡 Try it at home

Measure a table in hand spans and in spoons. Which gives the bigger number?

Estimate length

💡 An estimate is a smart guess using sizes you know.

A centimeter is about as wide as your finger. A meter is about one big step.

A new crayon is about 9 cm. A car is about 4 meters.

🧠 How to think about it

Picture a size you know. How many of them would fit? That is your estimate.

estimate: a careful guess
meter: about one big step long

🏡 Try it at home

Guess how many steps across a room. Then walk it. How close was your guess?

How much longer

💡 To find how much longer, subtract the shorter length from the longer one.

A pencil is 7 inches. A crayon is 3 inches. 7 − 3 = 4 inches longer.

On a ruler, start at 0. If you start at 1, count the spaces.

🧠 How to think about it

A crayon goes from 1 to 5. Count the spaces between: 4. It is 4 inches, not 5.

length: how long something is

🏡 Try it at home

Put a fork on a ruler starting at 1, not 0. Count the spaces to measure it.

Add and subtract on a number line

💡 A hop to the right adds and a hop to the left takes away.

Start at 8. Jump 6 to the right. You land on 14.

A hop from 5 to 12 shows 5 + 7 = 12.

🧠 How to think about it

Jump to the next ten first. 8 + 2 = 10. Then 4 more lands on 14.

number line: a line with numbers in order

🏡 Try it at home

Tape numbers 0 to 20 on the floor. Hop along to solve 9 + 5.

Bar graphs

Favorite snack

Apples

8

Cookies

4

💡 A bar graph shows each group as a bar, so you can count and compare.

Read the number at the top of each bar.

To find how many more, subtract. To find how many in all, add every bar.

🧠 How to think about it

Apples 8, cookies 4. How many more apples? 8 − 4 = 4. Read carefully before you add or subtract.

bar graph: a graph with bars to show amounts
line plot: a number line with an X for each thing measured

🏡 Try it at home

Count the cups, plates, and bowls in the kitchen. Draw a bar for each.