What is the maximum efficiency altitude for Turbojet Engines?

Turbojet engines achieve maximum efficiency at higher altitudes due to the thinner air, which allows them to operate more effectively. At around 36,000 feet, the balance of thrust-to-drag ratio and fuel efficiency tends to be optimized for these engines. This altitude allows turbojets to take advantage of increased speeds and reduced drag in the upper atmosphere while maintaining sufficient engine performance.

The other altitudes listed may not correspond to the sweet spot for turbojet efficiency. While some engines can perform at higher altitudes, they typically do not reach peak performance and efficiency until around 36,000 feet. Below this altitude, engines face greater air density, increasing drag, which can negatively impact their efficiency.