A worked example
A 5 GB file at 100 Mbps takes an ideal 6 minutes 40 seconds. With an 80% effective-rate assumption, the estimate is 8 minutes 20 seconds. The same number entered as 5 GiB represents more bytes and therefore takes longer.
For uploads, use your upload rate rather than the download rate advertised on the Internet plan. If you already know the sustained application throughput, choose its units carefully and use 100% for the direct estimate.