alam ko may formula for this, kung gusto mo ang sample size in statistical way, but for that you need to consider your preffered margin of error, confidence level, standard deviation of the population etc.
pero usually magfofocus ako dito sa standard deviation nung groups, why? kasi if mataas yong starndard deviation nung groups mo , it means yong data mo is dispersed or kalat, so youll need larger size,
you can check this vid btw : https://www.YøùTùbé.com/watch?v=Z2dKK1xicgs