Measure length using metric units

Length is quantified by comparing an object’s extent with equal metric units—millimeters, centimeters, meters, or kilometers—so measurement is the number of units that fit without gaps or overlaps. The learner reads rulers and other scales from zero, selects a sensible unit, estimates and records measurements, and relates units through 10-based equivalences (10 mm = 1 cm, 100 cm = 1 m, 1,000 m = 1 km), including conversions within this system; decimal-based precision and compound-unit conversions are beyond this scope.

Detailed Explanation: Measure length using metric units

Choose a metric unit that makes sense for the object:

Millimeters (mm): very small lengths
Centimeters (cm): small objects
Meters (m): larger objects or distances
Kilometers (km): long distances

To measure with a ruler:

Estimate the length.
Place the object’s end at the ruler’s 0 mark.
Keep the object straight along the ruler.
Read the mark at the other end.
Write the number and the unit.

Example

A crayon is placed beside a ruler. Its left end is at $0$ and its right end is at the $6$ -centimeter mark.

The crayon’s length is $6$ centimeters.
We write this as $\boxed{6\text{ cm}}$ .

To express the same length in millimeters, use the fact that

10\text{ mm}=1\text{ cm}.

So,

6\text{ cm}=6\times 10\text{ mm}=60\text{ mm}.

The crayon is $6\text{ cm}$ , or $60\text{ mm}$ , long.

Learn by doing: Measure length using metric units

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Measure with Ruler (metric) - Millimeters (5s) from Middle

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