A microbial growth can be measured indirectly by using
turbidometry methods. Microbial growth can be observed by the
intensity or turbidity of the solution/ growth medium. A
spectrophotometer can measure the turbidity of a solution and
giving an absorbance value directly proportional to the
concentration of microbial cells.
The microbial cell mass can also be weighed in dry or wet form
by discarding the solution and leaving the cell mass.
One can also measure the cell mass by measuring the oxygen
content, nutrient utilization, acid production, secondary
metabolite production, etc.
Microbial cells can also be counted using a scintillation
counter. One can also use hemocytometer.
Indirect labeling and counting of cells is another indirect
approach of measuring microbial growth.