Your goggles should fit comfortably with your goggle strap over the helmet. There should be no gap between the top of your goggles and the helmets (the so called "gaper gap"). The Sweet Protection goggles ensures a perfect fit to your helmets. The fit might vary depending on the the size and shape of your head. Please see this article to ensure you choose the right goggles for your helmet: Goggles Guide
For other manufacturers we can’t recommend the best possible fit other than to encourage you to try in store.