Common Core Math Vocabulary

Ruler - Definition with Examples

What is a Ruler?

Ruler Definition: A ruler is a tool used to measure lengths and draw straight lines.

Ruler with object

Rulers are available in both metric and customary units. Most commonly used rulers in classrooms is a ruler with centimeters on one side and inches on the other.

Ruler with centimeters and millimeter


Reading a Ruler

Reading Centimeters: A centimeter is smaller than an inch. They are the long lines below which the numbers are written.

Reading Centimeters on ruler

Reading Millimeters: A millimeter is smaller than a centimeter. The smaller lines between each centimeter line represent a millimeter mark.

10 millimeters = 1 centimeter


Reading Millimeters on ruler

Reading Inches: An inch is bigger than a centimeter. These are the larger lines on the side opposite to where centimeters and millimeters are marked.

Reading Inches on ruler


Measuring Objects Using Rulers 

Objects on a ruler are measured by putting one end of the object on 0 and aligning the object straight along the edges of the ruler. The mark where the other end of the object ends is the length of the object.

Measuring Objects Using Rulers

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