I found this chart helpful when purchasing beads for my jewelry projects. It helps take some doubt out of my purchases. It is always a good idea to purchase a few more extra beads then you think you really need.

Approximate Number of Beads Needed for Various Strand Lengths:

      Bead Size                       STRAND LENGTH

                            1"       4"     16"    20"    24"    28"    32"

• 3mm        8.46    33.8    136    170    204    237    272
• 4mm        6.35    25.4    102    127    153    178    204
• 5mm        5.08    20.32    82    102    125    143    164
• 6mm        4.23    16.9      68      84    101    118    136
• 7mm        3.62    14.4      58      70     86     101    116
• 8mm        3.17    12.68    51      64     76       89    102
• 10mm      2.54    10.16    41      51     61       71      82
• 12mm      2.11      8.44    34      42     51       59      68
• 14mm      1.81      7.24    29      36     43       50      58
• 16mm      1.58      6.32    25      32     38       44      50
• 18mm      1.41      5.64    23      28     34       39      46