code: public function getMaxUploadFileSize()
  	{
  		$objResult = Database::getInstance()->prepare("SELECT MAX(maxlength) AS maxlength FROM tl_form_field WHERE pid=? AND invisible='' AND type='upload' AND maxlength>0")
  											 ->execute($this->id);
  
  		if ($objResult->numRows > 0 && $objResult->maxlength > 0)
  		{
  			return $objResult->maxlength;
  		}
  		else
  		{
  			return Config::get('maxFileSize');
  		}
  	}
docs: Get the maximum file size that is allowed for file uploads
  
  @return integer The maximum file size in bytes