The only way to ensure the best possible fit is to physically try on the helmet prior to purchase. To assist you with this process SCOTT provides a sizing chart. To use the sizing chart measure your head size by passing a tape measure around your head, approximately 2 cm above the eyebrow line. Select the helmet size that closest matches the measurement. Since this process is not always accurate and helmet sizes do not always match perfectly with this basic measurement, it is important to select a helmet size that fits snugly, but without pressure points.