One size will fit most, as these are a CUFF style bracelet so they are opened ended, not a round closed circle bangle. It measures about 6" long with about a one inch gap that can be pinched tighter or pulled apart to fit perfectly.
Measurements-
Clare: 4.5mm
Jeannie: 5mm
Farrah: 4mm
Robin: 4mm
Mandy: 6.5mm
Hope: 5.5mm
Bella: 5mm
Angie: 8mm