Just before plating, after cold medium has been added to the trypsinized cells,
mix 0.1 mL cell suspension with 0.1 mL 0.4% trypan blue. Live cells will not take up trypan blue. (Use a different dilution factor if cells are uncountable)
inject 10 uL to one side of the hemocytometer (see image attached below).
Inspect at 10x.
Count the number of live (clear) cells in all 9 squares of the hemocyometer. (Volume = 3mm * 3 mm * 0.1 mm = 0.9 uL) (Count in 4 1mm x 1mm squares if cells are very numerous)
Calculate the live cell concentration (# live cells * 1.11)/1uL for 9 squares,
(# live cells * 2.5/uL for 4 squares)
correct for dilution factor