Lesson objective: Measure length following the rules for measuring with length units.

This lesson helps to build fluency with measuring with length units. The "Rules for Measuring Length" are used here because these rules support how to measure with length units accurately. This work develops students' understanding that the length measurement is equal to the number of same-size length units that span an object with no gaps or overlaps.

Students engage in Mathematical Practice #2 (reason abstractly and quantitatively) as they measure with length units and make approximations when the length units and the object they are measuring do not exactly align; Mathematical Practice #5 (use appropriate tools strategically) as they use length units to measure length; and Mathematical Practice #6 (attend to precision) as they work with the non-standard length units to determine the length of the object being measured. Students will evaluate worked examples to determine if the length has been measured accurately with the given length units.

**Key vocabulary:**

- accurately
- gaps
- length measurement
- length unit
- overlaps
- same-size
- span

**Special materials needed:**

- non-standard length units (blocks, building cubes, paper clips)
- items to measure (e.g. strips of paper)