How to Read a Ruler

Rulers are basic measurement tools. Standard rulers allow people to read measurements in either the metric (meters, centimeters, or millimeters) or the English (miles, yards, or inches) system.

Rulers can be made using a number of materials such as wood, metal, and plastic. They are often 12 inches (1 foot or 30.48 centimeters) long with varying thickness. The markings used for measurements are placed on its sides. Some rulers have the two measurement systems on different faces while others mark both on the same face but on different sides.

Materials to Prepare

  • pencil
  • piece of paper
  • 12-inch ruler

How to Measure in Centimeters and Millimeters

  1. Determine the English system side. In some rulers, the side is labeled. If not, check the markings on the face. The distance between lines should be smaller than the other side. This is because a centimeter is less than one inch. One inch is equal to 2.54 centimeters.
  2. There are 9 lines between each centimeter. These lines represent one millimeter (mm) each. There are 10 millimeters in one centimeter.
  3. Test your ruler-reading skills by marking two points on a piece of paper. Connect the two points with a straight line. Make sure that the two points don’t exceed the length of the ruler.
  4. Place your ruler beside the line. Put the beginning of the ruler at one end of the line. Look at the number on the ruler where the line ends. Note the number where the line ends. If the line stops between two numbers, note the lower number. If it stopped between 10 and 11, write down 10. This is the measurement in centimeters.
  5. If the line ends between two numbers, take note of the markings between the two numbers which connote millimeters. If the end of the line lies on the fifth mark, it means that there are five millimeters between your mark and the big number.
  6. Combine the two measurements you made to get the exact length of the line. In the example given, the length of the line is 10 centimeters and five millimeters. You can write it in decimal form: 10.5 cm.

How to Measure in Inches

  1. Determine the side of the ruler that has the markings in inches. This is the side of the ruler with the main numbers 1 to 12.
  2. Locate the number on the point where your line ends. It may end exactly on one of the big numbers or in between two big numbers. If it lands between two of the big numbers, note the smaller one.
  3. Count the smaller lines between the big numbers. There are seven lines in between the markings for inches. Each of these small marks measures 1/8 of an inch.
  4. Combine the two numbers. If the point of the end of your line stopped between four and five and at the first mark of the smaller line, your reading should be: 4 and 1/8 inches.

If you want to check if your measurements are accurate, you can convert the measurements. First, measure the line in inches. Multiply the result by 2.54 to convert it into centimeters.

Measure the line in centimeters next. If the measurement in centimeters is the same as the converted number, then you measured it correctly.