4mm (4 millimeters ~ click for samples) 100 beads per 16" strand
6mm (6 millimeters - click for samples)
65 beads per 16" strand
The higher the number, the smaller the bead.Seed beads sizes are stated as strung beads per inch.3/0 beads would be 4 per inch, about 1/4 inch thick each. (Crow rollers, pony beads)
6/0 beads would be about 8 per inch, or 1/8 inch thick each. (The popular "e" bead)
15/0 beads would be 18 per inch, 1/18 inch thick each. (Tiny)
This is a general guideline - seed bead sizes are still a little tricky, even for me sometimes!