Seed beads are classified by a number that refers to their size, e.g. 3/0, 6/0, 8/0, 11/0 and 15/0. The most important key to understanding the size of seed beads is the concept that the smaller the number, the larger the bead. This means that a 3/0 seed bead is larger than an 8/0 seed bead.
| Brand | Size | ∅ outside | ∅ inside |
| Miyuki | 15/0 | 1,5 mm | 0,7 mm |
| Miyuki | 11/0 | 2,0 mm | 0,8 mm |
| Miyuki | 8/0 | 3,0 mm | 1,1 mm |
| Miyuki | 6/0 | 4,0 mm | 1,5 mm |
| Toho | 15/0 | 1,5 mm | 0,6 mm |
| Toho | 11/0 | 2,2 mm | 0,8 mm |
| Toho | 8/0 | 3,0 mm | 1,1 mm |
| Toho | 6/0 | 4,0 mm | 1,2 mm |
| Toho | 3/0 | 5,5 mm | 2,5 mm |
