The number of beads on a string varies because of the size of the bead and also the length of the string.  Most beads are sold in 16" lengths.  Below is a guide to how many beads you may get on a 16" length. 

Bead size (mm)       Quantity

2mm                        203 beads                                                     

3mm                        136 beads

4mm                        100 beads

6mm                        67 beads

8mm                        50 beads

10mm                      41 beads

12mm                      34 beads

Please note this is approximate as some beads may vary very slightly in size depending on material and the manufacturing process.  There may also be gaps or spacers between the beads.