Measuring length

What is this skill?

Measuring length in second grade means using rulers, yardsticks and meter sticks to measure objects in inches, feet, yards, centimeters and meters, and solving problems with those lengths. Children compare lengths ("How much longer is the pencil than the crayon?"), add lengths laid end to end, and choose a sensible unit for the thing being measured.

They also learn that the size of the unit matters. A book might be measured in inches or centimeters, a door in feet, a bus in meters and a football field in yards. A smaller unit gives a bigger number for the same object, because more of the small units fit along it. A ruler is really a number line, which links measurement to the addition and subtraction children already know.

Why it matters

Measurement is math that children can hold in their hands, and it is used in cooking, building, sewing, sports and science. Learning to measure accurately, starting at zero and reading the right mark, is a practical skill on its own.

It also deepens number sense. Finding how much longer one ribbon is than another is a subtraction problem; joining two lengths is addition. Choosing a sensible unit builds a feel for sizes, which helps children judge whether an answer is reasonable, such as noticing that a pencil cannot be 15 feet long.

Common mistakes

• Starting a measurement at the 1 on the ruler instead of at the 0 mark, which adds an extra unit. Show your child where zero is, which on some rulers is not at the very edge.
• Mixing up inches and centimeters on a ruler that has both. Point out which side is which before measuring.
• Thinking a bigger number always means a longer object, even when the units are different. Compare the same object measured in inches and centimeters to see why.
• Leaving gaps or overlaps when measuring with repeated objects like paper clips. Line them up end to end with no spaces.

How to help at home

• Give your child a ruler or tape measure and a list of things to measure: a spoon, a shoe, the table, a pet’s bed. Record the lengths together.
• Estimate first, then measure. "How many inches long do you think your foot is?" Over time, estimates get closer.
• Compare and combine: measure two toys, then ask how much longer one is, and how long they would be laid end to end.
• Talk about choosing units: "Would you measure the driveway in inches or feet? What about a grasshopper?"

Worked examples

These are real questions from the Tutorsaurus measuring length practice, with the answers worked out.

1. Example 1

   A pencil is 8 inches long. A crayon is 7 inches long. How much longer is the pencil?

   Answer: 1 in. 8 − 7 = 1 inches.

2. Example 2

   Two ribbons are 4 inches and 8 inches. Laid end to end, how long are they?

   Answer: 12 in. 4 + 8 = 12 inches.

3. Example 3

   Which unit is best to measure a book?

   Choices: meters, miles, centimeters, inches

   Answer: inches. inches fit a book best. Small things take small units, big things take big units.