url = http://www.autohotkey.net/~Lexikos/AutoHotkey_L/AutoHotkey_L_Install.exe
 
MsgBox, % GetFileSizeFromInternet(url)   ; размер в байтах
 
GetFileSizeFromInternet(url, ProxyName = "", ProxyBypass = "")
{
   INTERNET_OPEN_TYPE_DIRECT = 1
   INTERNET_OPEN_TYPE_PROXY = 3
   AccessType := ProxyName ? INTERNET_OPEN_TYPE_DIRECT : INTERNET_OPEN_TYPE_PROXY
   INTERNET_FLAG_RELOAD = 0x80000000
   HTTP_QUERY_CONTENT_LENGTH = 5
   coding := A_IsUnicode ? "W" : "A"
 
   hModule := DllCall("LoadLibrary", Str, "wininet.dll")
   hInternet := DllCall("wininet\InternetOpen" . coding
                  , Str, ""   
                  , UInt, INTERNET_OPEN_TYPE_DIRECT
                  , Str, ""
                  , Str, ""
                  , UInt, 0)
   if !hInternet
   {
      Error := A_LastError
      DllCall("FreeLibrary", UInt, hModule)
      Return "Ошибка " . Error
   }
 
   hFile := DllCall("wininet\InternetOpenUrl" . coding
               , UInt, hInternet
               , Str, url
               , Str, ""
               , UInt, 0
               , UInt, INTERNET_FLAG_RELOAD
               , UInt, 0)
   if !hFile
   {
      Error := A_LastError
      DllCall("wininet\InternetCloseHandle", UInt, hInternet)
      DllCall("FreeLibrary", UInt, hModule)
      Return "Ошибка " . Error
   }
 
   VarSetCapacity(buff, 64)
   VarSetCapacity(bufflen, 2)
   Loop 4
   {
      success := DllCall("wininet\HttpQueryInfo" . coding
                  , UInt, hFile
                  , UInt, HTTP_QUERY_CONTENT_LENGTH
                  , UInt, &buff
                  , UInt, &bufflen
                  , UInt, 0)
      if success
         Break
   }
   Result := success ? StrGet(&buff) : "Невозможно извлечь информацию"
 
   DllCall("wininet\InternetCloseHandle", UInt, hInternet)
   DllCall("wininet\InternetCloseHandle", UInt, hFile)
   DllCall("FreeLibrary", UInt, hModule)
 
   Return Result
}