You can use the Trypan Blue Dye method. 10 ul of cell is mixed with 10 ul of trypan blue. 10 ul of the mixture is loaded into the hemocytometer and the large squares are counted and divided by 4 to get average of all four squares. We then calculate the total cells by the formula:

(cell average in all square) X 2 X Dilution Factor.

Dead cells will stain blue while live cells will remain unstained. For whole cell in the flask, you may count both stained and unstained cells.

see here, maybe it'useful

https://cellculture.altervista.org/cell-counting-hemocytometer/