We want to conduct a multi-center randomized clinical trial with two arms (2 treatments : a superiority trial) stratified on three centers (three sites).

The primary outcome variable is a continuous variable (presented as mean, sd). How can i estimate the sample size needed for this stratified trials (for each center)?

I found many packages in R that deal with sample size estimation, but i do not I did not find any that is suitable for this analysis.

Thank you