Explain what a centimeter is. State that your thumb is approximately one centimeter wide. Centimeter is abbreviated as cm. Take a ruler and point to what a centimeter is. You may have students measure the width of their thumb to demonstrate that this is about a centimeter. Next you set several objects on a table, of which some are about one centimeter and some are larger. Have the students indicate which of the objects are about one centimeter. Then they must find other objects in the classroom that are about a centimeter. Afterwards, you show an image on the interactive whiteboard. Explain that a number of objects in the image are about one centimeter in real life. Have the students find these objects and drag them to the basket. Remind the students that they can compare the objects to the width of their thumb. If it is about the same width, then the object is one centimeter. Afterwards you show an image and the students indicate whether it is one, ten, or one hundred centimeters.

To check whether the students understand what a centimeter is, you can ask the following questions:

- How is centimeter abbreviated?

- What is about one centimeter?