What is Units of length? — Mathematics

Definition 19.1 Primary & Middle School Mathematics · Chapter 19 — Measuring

The basic unit of length is the meter (m). For small lengths: the centimeter (cm) and the millimeter (mm); for long distances: the kilometer (km).

1 \text{ m} = 100 \text{ cm}, \qquad 1 \text{ cm} = 10 \text{ mm}, \qquad 1 \text{ km} = 1\,000 \text{ m}.

Reading a ruler: big marks for centimeters, small marks for millimeters. The object starts at the 0 mark — not at the edge of the ruler! — and ends at the 6th small mark after the 3. — Reading a ruler: big marks for centimeters, small marks for millimeters. The object starts at the $0$ mark — not at the edge of the ruler! — and ends at the $6$ th small mark after the $3$ .

Examples

Example 19.2 (Choosing the right unit)

An ant: about $5$ mm. A pencil: about $18$ cm. A door: about $2$ m. A walk to the next village: about $3$ km. Giving “the length of a pencil is $18$ ” means nothing — the unit is part of the answer.

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