A bike helmet should fit snugly on your head, sitting level and low on your forehead. It shouldn’t move around easily, but it also shouldn’t be uncomfortably tight. Achieving the perfect fit involves adjusting various components of the helmet, including the straps, padding, and retention system.
Measuring Your Head
Before purchasing a bike helmet, you need to know your head circum... https://www.uniquebikezone.com/how-bike-helmet-should-fit/#more-1783