Depends on what effect size or power you are looking for and/or other factors like variance in the data (standard deviation), etc. There are some different way

Depends on what effect size or power you are looking for and/or other factors like variance in the data (standard deviation), etc. There are some different ways to calculate sample sizes here: https://en.wikipedia.org/wiki/Sample_size_determination https://en.wikipedia.org/wiki/Sample_size_determination or google: sample size calculator