* Atomic Mass: The atomic mass of helium is 4.002602 amu (atomic mass units). This is the average mass of a helium atom, taking into account the relative abundance of its isotopes.

* Molar Mass: The molar mass of helium is 4.002602 g/mol. This means that one mole of helium atoms has a mass of 4.002602 grams.

* Mass of a Single Helium Atom: The mass of a single helium atom is 6.646476 x 10^-27 kg. This is calculated using the atomic mass and Avogadro's number.

So, to be more specific, please clarify what you mean by "mass of helium"!