下面的函數用來計算某個文件目錄所占的字節數：

REM 函數返回值為目錄所占字節數
Function DirUsedBytes(ByVal dirName As String) As Long
          Dim FileName As String
          Dim FileSize As Currency
          If Right$(dirName, 1) <> "/" Then
               dirName = dirName & "/"
          Endif
          FileSize = 0
          FileName = Dir$(dirName & "*.*")
          Do While FileName <> ""
                 FileSize = FileSize +  FileLen(dirName & FileName)
                FileName = Dir$
          Loop
          DirUsedBytes = FileSize
end function

使用方法：

MsgBox DirUsedBytes("D:/musics")