Relative isotopic mass is similar to atomic mass and has exactly the same numerical value as atomic mass, whenever atomic mass is expressed in unified atomic mass units, whereas relative isotopic mass is a pure number with no units.
Relative isotopic mass is similar to atomic mass. Relative isotopic mass has exactly the same numerical value as atomic mass. Whereas relative isotopic mass is a pure number with no units. This was what atomic mass is expressed in unified atomic mass units.