They are available in a wide range of sizes, measured in millimeters (mm) or in a numbering system. The most common seed bead sizes are:
- Size 11/0 (2.5 mm diameter)
- Size 10/0 (3.0 mm diameter)
- Size 8/0 (3.5 mm diameter)
- Size 6/0 (4.0 mm diameter)
The number before the slash (/) refers to the number of beads per inch, and the number after the slash refers to the number of times the bead must be strung to make an inch. The larger the first number, the smaller the bead.