Interstellar dust grains typically range in size from a few nanometers to a few micrometers.

Here's a breakdown:

* Smallest: Around 10 nanometers (10^-8 meters)

* Largest: Up to a few micrometers (10^-6 meters)

It's important to note that the distribution of sizes is not uniform. There are significantly more smaller grains than larger ones. This means the average size is likely closer to the smaller end of the range.