Measurement & Data
Measuring in Standard Units
Measuring the length of an object using inches, feet, centimeters, and meters.
Measuring with Real Units
In Grade 1, length was measured using everyday objects like paperclips, which gave different-sized results depending on which object was used. Standard units — like inches, feet, centimeters, and meters — solve that problem, because everyone using the same standard unit gets the same measurement.
Definition — Standard Unit
A ruler is marked with standard length units so an object can be measured directly by lining it up with the marks. Inches and feet make up the customary system used in the United States; centimeters and meters make up the metric system used in most of the rest of the world.
Worked Example — Measuring with a Ruler in Inches
Worked Example — Choosing an Appropriate Unit
Tip
Common Mistakes
Lining an object up with the edge of the ruler instead of the ruler's 0 mark, which can be in a slightly different place.
Always find the 0 mark specifically and start measuring from there, even if it isn't exactly at the physical edge of the ruler.
Mixing customary units (inches, feet) with metric units (centimeters, meters) within the same measurement.
Pick one system of units and stay consistent throughout a single measurement — inches and centimeters measure the same real-world length but give different numbers.
Key Takeaways
- Standard units, unlike everyday objects, always mean the same fixed length for everyone.
- A ruler measures length directly by lining an object up with its 0 mark.
- Choosing a reasonably sized unit, like feet instead of inches for a long object, keeps measurements easy to read.
Summary
Measuring in standard units gives length a fixed, shareable meaning. The next lesson puts that measuring skill to work, solving word problems that involve adding and subtracting lengths.
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