That's a great question! Altocirrus clouds are considered high-level clouds, meaning they form in the upper troposphere, between 5,000 and 13,000 feet (1.5 - 4 km) above the Earth's surface.

However, they are not the highest clouds. That honor goes to cirrus clouds, which are also high-level but can form even higher, up to 40,000 feet (12 km) or more.

So, while altocirrus clouds are high, they're not quite as lofty as their cirrus cousins.