Sizes are with the velcro secured evenly, neck velcro is 7cm long allowing an adjustment of approx. 3 cm either way (eg. 24cm neck = 21cm-27cm adjustment), Abdomen velcro is 8cm long, allowing 4cm adjustment either way (eg. 38cm abdomen = 34cm-42cm adjustment).  This allows for plenty of velcro to be secured together to ensure it’s secure.