Grade 1Length, Time and Data1.MD.A.2

Measuring with Same-Size Units

Lay units end to end with no gaps or overlaps.

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To say how long something is, use same-size units, like cubes or paper clips. You can compare lengths and count to 20, so you are ready.

The pencil is 6 cubes long. The crayon is 5 paper clips long.

Key idea

Lay the units end to end, with no gaps and no overlaps. The number of units is the length.

Why it works

Every unit is the same size, so counting units tells how much length there is. A gap leaves length uncounted. An overlap counts some length twice.

Worked example: Cubes

A crayon lines up with 5 cubes, end to end. How long is it?
  1. The cubes touch end to end, with no gaps.
  2. Count them: 5.
  3. The crayon is 5 cubes long.

Answer: 5 cubes

The first pencil is measured the right way. The second has a gap, so it looks only 5 cubes long.

Common mistake

Leaving gaps, overlapping units, or mixing big and small units. Check that the units touch, none sit on top of each other, and all are the same size.
For grown-ups: Measure toys with paper clips or blocks together. Ask, “Are there any gaps?”

Practice

Pass with 3 right answers, the last 2 in a row. Each right answer earns 1 XP.

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Sources and further reading

  • Common Core State Standards for Mathematics, Grade 1, 1.MD.A.2: express length as a whole number of same-size units laid end to end with no gaps or overlaps
  • Institute of Education Sciences practice guide: Assisting Students Struggling with Mathematics: Intervention in the Elementary Grades (WWC 2021006)
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