How to read measurements on a ruler scale

Written by christine lehman
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How to read measurements on a ruler scale
This ruler has both English and metric scales. (ruler and pencil image by Hao Wang from

Rulers measure distances in either metric or English units. Rulers are made of a variety of substances, making their use easy regardless of what you are measuring. For example, straight rulers are useful for measuring wood or paper, while a tape measure is better for measuring a waistline. Reading a scale is done similarly, regardless of the ruler's scale or type.

Skill level:

Things you need

  • Ruler

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  1. 1

    Align the left edge of the ruler with the edge of the item you are measuring. Occasionally there will be a small space on the ruler to the left of the first official line, which will be marked with a zero or arrow. If this is the case, line up the first line with the edge of the object. Proper alignment will ensure a more accurate reading.

  2. 2

    Stretch the ruler along the length of the object. If the object is irregularly shaped -- e.g., a round pipe -- you may need to use a more flexible ruler, like a measuring tape. Making sure the ruler lays straight and flush with the surface of the object will increase accuracy.

  3. 3

    Observe the ruler at the opposite end of the object. Find the line on the ruler closest to this end. Read the first whole number on the ruler you see to the left of this line and write it down. If the line on the ruler closest to the end of the object happens to line up directly with a whole number, this is your measurement. If not, your measurement will contain either a fraction or decimal point, depending on whether your ruler is English or metric, respectively.

  4. 4

    Examine the small markings on the ruler that follow the whole number. If the ruler is English, the whole numbers are inches and each of these small marks equals one-eighth or one-sixteenth of an inch. To be sure, count the number of these small lines occurring within an inch. Then, count how many of these small lines are between the whole number and the end of the object and put this number over either eight or 16, depending on the scale. For example, if the small ruler markings represent one-sixteenth of an inch and you count three of them, your measurement will be the whole number plus three-sixteenths. Reduce the fraction if possible; e.g., rather than eight-sixteenths, write one-half. If the ruler is metric, each whole number will represent a centimetre and the small lines between are millimetres. Count the number of these small lines between the last whole number and the end of the object. Place this number to the right of a decimal point after the whole number; e.g., 3.4cm.

Tips and warnings

  • If the lines on a ruler are thick, use the centre of the line to attain your measurement. If the object falls between two lines and accuracy is important, get a ruler with a finer scale.

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