Place your ruler on your work space. Select an item to measure. A good option is an object that is long and flat -- such as a pencil.
Place the pencil against the ruler and above it. The closer the object is to the ruler, the easier it may be to see precise measurements.
Determine whether you are using a 1/8-inch ruler or a 1/16th-inch ruler. To do this, count the number of vertical lines in between the numerals. If you count seven lines, you have a 1/8th-inch ruler, and if you count 15 lines, you have a 1/16th-inch ruler.
Locate the numeral that is closest to the end of the pencil (or the tip of the pencil) without going past the pencil. For example, on a standard English ruler, you likely will see numerals 1 thru 12, with each numeral representing an inch amount. Write down that number. For our purposes, let us say the number you write down is 4.
Count the number of lines past the numeral you wrote down all the way to the end of the pencil. Add them up. For example, if you have a 1/8th-inch ruler and you count 6 lines, then your calculation is 6/8 inches. This reduces to ¾ inches.
Add the fraction to the whole inch number you wrote down. In this example, the pencil is 4 ¾ inches long.