This value will range from 0.0 to 1.0. The value is an estimate based on the total number of bytes expected to be received for a download. If you need a more accurate progress information you can connect to #WebKitDownload::received-data signal to track the progress.
Download.estimatedProgress
double estimatedProgress() @propertyGet estimatedProgress property.
Returns
An estimate of the percent completion for the download operation.