IPhone : Keep UITableViewCell height in different IPhone screen

I don't understand how to keep heigt of rows in UITableViewCell in different screen sizes. I've setted to 50 my custom row Height, in the cell's xib and in the method:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {

return 50;

}

But in IPhone 5 and iphone 6 Plus I'm seeing 8 table cell in the screen. I don't want to. I want the same row height and a lot of more rows in the IPhone 6 plus, like facebook app. How to achieve that?