Rubber bracelets are sometimes made to be very large so they'll fit just about anyone. You may end up with one that you like, but it's too large for your wrist. If you want to wear your favorite rubber bracelet without it falling off of your wrist, you can shrink it using materials you can find in any craft store. You must take care, though, to not make the bracelet too small.
Measure your wrist with a tape measure and add a one-half inch to this length so you can fit the bracelet over the widest part of your hand. Measure the circumference (all the way around) of the bracelet with the tape measure and subtract your wrist measurement (with the one-half inch added) from this measurement.
Cut out a bottom section of the bracelet at the length that you got from subtracting the size of your wrist from the circumference of the bracelet. Use a sharp pair of scissors.
Read the instructions on your package of rubber cement for drying times and particular use for the brand you bought. Glue the two cut ends of the bracelet together and allow the rubber cement to dry completely before putting the bracelet on.