Abstract <p>Spectrophotometric methods are frequently used to monitor growth and development in cyanobacteria cultures of toxicity studies. Chlorophyll-<i>a</i> measurement is one of the most important parameters for determining the growth in cyanobacteria cultures. In evaluating this parameter, extraction with solvents should primarily be carried out during the daily measurements. The use of this method causes both labor and material consumption. Since the chlorophyll-<i>a</i> content is related to the doubling time and initial culture concentration, it is possible to measure chlorophyll-<i>a</i> by modeling these values. Mathematical model analysis has gained importance in phycology studies due to advancements in hardware and software technologies. Microbial process modeling provides insights into the growth behavior of cyanobacteria and helps obtain effective results in algal culture outputs. For this purpose, available data were adapted to the Gompertz, Logistic, Weibull, Exponential, and Richards models in multiple pesticide applications. The cases fit the models with the following percentages: 89.77% (Gompertz), 76.14% (Logistics), 65.91% (Richards), 81.82% (Weibull), and 93.18% (Stirling). While these cases indicate that sufficient culture conditions are provided to fit both the growth and exponential models, it is possible to accurately calculate values for the asymptote, lag phase, and doubling time. The doubling time of the chlorophyll-<i>a</i> content varies according to the initial concentration and the length of the growth rate. The formula correlation is based on the doubling time of growth parameters. There is an indirect relationship between OD560 and chlorophyll-<i>a</i> content. Using the regression formula obtained from the doubling time values of OD560 and chlorophyll-<i>a</i>, chlorophyll-<i>a</i> can be easily determined from OD560 in future studies.</p>