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How to Read a Ruler

Your ruler shouldn't be used only to draw a straight line. Make sense of all those little lines and take advantage of its intended use.


  • Step 1: Pick a side Pick a side to use for your measurement. One side measures 30 centimeters, and the other side of the ruler measures 12 inches.
  • Step 2: Multiply by 10 Multiply centimeters by 10 to calculate millimeters. For example, 1.2 centimeters equals 12 millimeters.
  • TIP: Centimeters are the longer marks on the metric side of the ruler; millimeters are the shorter marks.
  • Step 3: Recognize the line differences Recognize the different line lengths on the English side of the ruler. The inch line is the longest line with the number next to it. The shorter lines represent fractions of an inch.
  • Step 4: Identify the 15 other lines Identify the other 15 lines. They decrease in size from 1/2 to 1/4 of an inch, all the way down to 1/16 of an inch.
  • TIP: Some rulers display measurements down to 1/64 of an inch.
  • Step 5: Convert to fractions Convert the fractions into decimals using a calculator. Divide the fraction of the inch and then add the whole number. The English side is more complicated than the metric side, since there are 12 inches in a foot rather than the increments of 10 used on the metric side, but once you have mastered the conversions, you can use your knowledge to measure just about any length.
  • FACT: The first recorded unit of measure was the cubit, developed by the Egyptians. The cubit was the length from a man's elbow to the end of his middle finger, about 20.6 inches.

You Will Need

  • Ruler
  • Calculator

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