How to find out size of session in ASP.NET from web application?

If you're trying to get the size of Session during runtime rather than in debug tracing, you might want to try something like this:

long totalSessionBytes = 0;
BinaryFormatter b = new BinaryFormatter();
MemoryStream m;
foreach(var obj in Session) 
{
  m = new MemoryStream();
  b.Serialize(m, obj);
  totalSessionBytes += m.Length;
}

(Inspired by http://www.codeproject.com/KB/session/exploresessionandcache.aspx)

The code in the answer above kept giving me the same number. Here is the code that finally worked for me:

private void ShowSessionSize()
{
    Page.Trace.Write("Session Trace Info");

    long totalSessionBytes = 0;
    System.Runtime.Serialization.Formatters.Binary.BinaryFormatter b = 
        new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
    System.IO.MemoryStream m;
    foreach (string key in Session)
    {
        var obj = Session[key];
        m = new System.IO.MemoryStream();
        b.Serialize(m, obj);
        totalSessionBytes += m.Length;

        Page.Trace.Write(String.Format("{0}: {1:n} kb", key, m.Length / 1024));
    }

    Page.Trace.Write(String.Format("Total Size of Session Data: {0:n} kb", 
       totalSessionBytes / 1024));
}