How to Measure Length Correctly with a Ruler

Khan Academy

This video provides a practical and interactive tutorial on measuring length using standard units like centimeters and meters. Through a series of digital exercises, the narrator demonstrates the correct techniques for using a ruler, emphasizing the importance of alignment and precision. The video progresses from conceptual multiple-choice questions about proper measurement methods to hands-on examples where the narrator manipulates a digital ruler to measure various objects, such as an eraser, a building, a backyard scene, and a tray of cookies. Key themes include the fundamental rules of measurement: avoiding gaps between units, preventing overlaps, and aligning the starting point of the ruler (the zero mark) with the edge of the object. The video also clarifies geometric vocabulary, specifically defining "length" as the longest dimension of an object when distinguishing it from width. The narration models mathematical thinking by verbalizing the reasoning behind accepting or rejecting specific measurement setups. For educators, this video serves as an excellent tool for introducing or reinforcing early measurement skills in primary grades. It directly addresses common student errors, such as starting measurements at the wrong point or failing to measure end-to-end. Teachers can use this video to model best practices before having students practice with physical rulers, or as a remediation tool for students struggling with the concept of continuous measurement units.