Hello Jonathan,
Actually, it is not possible to calculate the amount of visitors a Dedicated Server can handle due to various reasons. This depends on the applications you have on your dedicated server with the number of websites you are currently hosting on it. Alongwith this, the number of visitors visiting your website and the time for which they remain on the website also makes a difference.
If you are not sure about your requirements, you can consider a dedicated server with an average configuration and host your website on it. If your requirements increase in future, you can upgrade your dedicated server at any point of time
