The beads range in size. I have a chart which shows the actual size of the bead and its size relative to other Kazuri beads. The chart also gives a comparison to a common object for most of the beads. For example, the Pita Pat size is 22-24mm, which is about the size of a quarter.

Here's some help with millimeters:

10mm = is just shy of a half inch
20mm = about 3/4 of a inch
25mm = about an inch

Click here for the size chart