In the second film, 'How to Train Your Dragon 2', there's a scene where Hiccup and Toothless participate in a race against other dragons. During this race, Toothless displays incredible speed and agility, outpacing the other dragons and achieving a significant lead. While specific numbers are not provided, this scene clearly demonstrates the Night Fury's exceptional flying speed compared to other dragons in the franchise.
Additionally, the Night Fury's flight is characterized by its sleek, aerodynamic design and powerful wing structure. This suggests that it possesses the natural capabilities for reaching high speeds and maintaining stability during flight.
While specific figures for the Night Fury's speed are not available, it can be assumed that it can fly at speeds comparable to those observed in other fast-flying creatures in the real world, such as falcons or peregrine falcons, which can reach speeds of up to 200 miles per hour (322 kilometers per hour) during dives.