When it comes to extra-large bike helmets, there is no one-size-fits-all answer. The size of an extra-large bike helmet will depend on the brand and model of the helmet. However, most extra-large bike helmets will have a circumference of around 62 cm. So, if you're looking for an extra-large bike helmet, be sure to measure your head before you buy. And, if you're still not sure which size to get, err on the side of caution and go with the larger size. After all, it's better to be safe than sorry.