There are several ways through which one can identify the most appropriate sample size for a study. One old yet reliable method is using the Krejcie and Morgan formula (1970). https://www.kenpro.org/sample-size-determination-using-krejcie-and-morgan-table/

sample size can vary form 25 to 5000 depending on type of study and constraints and research too you are going to use. In general studies of population underlining assumption is infinite population that is normally distributed on its studied characteristic or parameter. Such things are not possible in actual life hence margin of error remain by which sample actually represent population. For nonparametric tests sample size like in T test or chi square test can be small say 25-75 samples .For z test above discussion applies.

Here is a note for you:

Determining the appropriate sample size is a critical aspect of research design, as it influences the reliability and validity of study findings. The ideal sample size depends on several factors, including the research objectives, study design, population size, desired confidence level, and acceptable margin of error.

Key Considerations for Sample Size Determination:

Sample Size Calculation:

For quantitative studies aiming for statistical analysis, the following formula is commonly used to calculate sample size:

n=Z2×p×(1−p)E2n = \frac{{Z^2 \times p \times (1 - p)}}{{E^2}}n=E2Z2×p×(1−p)​

Where:

• nnn = required sample size
• ZZZ = Z-score corresponding to the desired confidence level (e.g., 1.96 for 95% confidence)
• ppp = estimated proportion of the population possessing the attribute of interest
• EEE = acceptable margin of error

This formula assumes a large population. Adjustments may be necessary for smaller populations. Additionally, when the population standard deviation is unknown, a standard deviation of 0.5 is often used as a conservative estimate.

geopoll.com

Practical Steps:

By carefully considering these factors, researchers can determine an appropriate sample size that enhances the credibility and generalizability of their study findings.

Too, too, too general a question...

Following@

Todo depende del tipo de investigación que vas a realizar, puede ser de gran ayuda iniciar con una muestra piloto si la muestra es demasiada grande, para así evaluar la viabilidad, e identificar posibles problemas de diseño en el estudio principal.