The unit that measures the mass of a single atom is the atomic mass unit (amu).

Here's a bit more about it:

* Definition: One atomic mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom.

* Convenient: It's a very small unit, making it easier to express the masses of tiny atoms.

* Not the same as grams: It's important to remember that amu is not the same as grams.

* Conversion: 1 amu is approximately equal to 1.66053906660 × 10^-27 kg.

Let me know if you have any other questions!