Lesson objective: Understand that the size of the unit impacts the number of units in a measured length.

Students bring prior knowledge of measurement from 2.MD.A.1. This prior knowledge is extended to reasoning about the relationship between the unit size and number of units in a measured length as students compare two measured lengths. A conceptual challenge students may encounter is understanding that the relationship is an inverse relationship.

The concept is developed through work with problems evaluating a task or situation in which students explore and analyze different measurement systems and the related units.

This work helps students deepen their understanding of equivalence because the inverse relationship shows that the smaller the measurement unit, the more units are needed in the measured length.

Students engage in Mathematical Practice 2 (Reason abstract and quantitatively) as they reason and make sense of the problems as they compare lengths measured using different units.

**Key vocabulary: **

- foot
- inch
- inverse
- length
- meter
- meter stick
- relationship
- ruler
- tape measure
- tool
- unit of measure
- yard
- yardstick

**Special materials needed:**

- centimeter ruler
- inch ruler
- meter stick
- ruler
- tape measure
- yardstick