Growth is one of the characteristic of all living organisms? Do unicellular organisms also grow? If so, what are the parameters?

Characteristics of growth are increase in mass of the cell and increase in cell number.

Yes, unicellular organisms also grow. When it comes to a multicellular and unicellular organisms, it grows by dividing its cells or undergoing cell division by increase in cell mass as well as increase in number of cells. This can be observed by observing the cells under microscope and counting the increase in number of cells.