Common Core Math Vocabulary

Ruler - Definition with Examples

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What is a ruler? 
A ruler can be defined as a tool or device used to measure length and draw straight lines.

Rulers can be used to measure lengths in both metric and customary units. Here, the ruler is marked in centimeters (cms) along the top and in inches along the bottom. 

Ruler with hash marks in Metric centimeter customary inches units of length

The marks or intervals on a ruler are called hash marks.

Measuring Objects using a Ruler: 
To measure the length of an object, place the zero hash mark of the ruler exactly along one end of the object. Align the object you are measuring along the edge of the ruler. Note the hashmark on the ruler along which the other side of the object ends.

Here, the shoelace is 17.6cms long in metric units of length, and 7 inches long in customary units of length. 

How to measure length of an object using a ruler

Reading a Ruler:

Reading Centimeters and Millimeters: A centimeter is smaller than an inch. The long hash marks under which numbers are written on the ruler denote centimeters.  
A millimeter is even smaller than a centimeter. The smaller hash marks between each centimeter represent millimeters. 

10-millimeter hash marks make 1 centimeter. 

Reading hash marks of ruler in centimeter and millimeter metric units

Reading Inches: An inch is bigger than a centimeter. The big long hash marks above which numbers are written on the opposite side of the centimeter ruler denote inches. 

Reading hash marks of ruler in inches customary units

  Fun Facts

  • The oldest preserved ruler is a copper alloy rod from c.2650 BCE, found by a German Archaeologist, while excavating at Nippur.
  • A ruler is also called a rule.
 

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Draw a long straight line,
Or measure the length of a vine.
All you need to do is align,
The ruler is a tool so fine!
 

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Give you child sticks or ribbons of different measures. Ask them to use the ruler correctly and note the length of each in both metric (cms/mms) and customary units (inches).
 

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