Number of cells in a morula is:

Once the zygote has reached the two-cell stage, it undergoes a series of mitotic divisions, increasing the numbers of cells. These cells, which become smaller with each cleavage division, are known as blastomere. After the third cleavage, however, blastomeres maximize their contact with each other, forming a compact ball of cells held together by tight junctions. This process of compaction, segregates inner cells, which communicate extensively by gap junctions, from outer cells. Approximately 3 days after feilization, cells of the compacted embryo divide again to form a 16-cell morula (mulberry). Ref: Langman's embryology 11th edition Chapter 3.