When cardboard is curled so the two sides of the wedge meet, it forms a cone. The larger the circle is, the taller the cone.
Making a cardboard cone takes only a few steps.
Step 1: Make a cardboard circle
Using a compass, draw a circle on cardboard. The distance from the center point to the outer edge is the cone's height. Cut out the circle using a utility knife.
Step 2: Cut the wedge
Draw a straight line from the center point to the circle's edge. Cut along that line. Curl the cardboard until the cone is the desired diameter. Mark that point. Uncurl the cardboard and draw a straight line from the center point to the mark. Cut along that line.
Step 3: Make the cone
Press the sides of the wedge together and glue or tape the cardboard to maintain the cone shape.