In this tutorial, we learn how to know the ruler. An inch ruler will have 12 inches on it. Each mark will be right next to these. Half of these marks will be a half an inch and the half of those with be an eighth. Half of this will be a sixteenth. On the other side of the ruler, you will see the metric system of the ruler, which is not used in the United States. It has centimeters listed on it instead of inches. To use the ruler, you will need to look at the mark it is on, then count the small marks to finish.