Transfer time
Monthly traffic and average bandwidth
Bits and bytes
Network speeds are quoted in bits per second (Mbps, Gbps) while file sizes are in bytes, and a byte is 8 bits. So a 100 Mbps connection moves at most 12.5 megabytes a second, and a 10 GB file takes at least 800 seconds, about 13 minutes. Speeds always use decimal prefixes (1 Mbps is 1,000,000 bits per second); sizes may be decimal (GB) or binary (GiB), so choose the unit your file manager shows.
Why real transfers are slower
Some of every link carries headers, acknowledgements and retransmissions rather than your data. On wired Ethernet, TCP/IP overhead is around 5%; Wi-Fi, VPNs and long-distance links lose more, and a single TCP stream over a high-latency path may not fill a fast link at all. Disk speed, server load and shared links also limit what you get. The overhead setting gives a realistic estimate; the result is still a best case.
Monthly transfer and bandwidth
Hosting plans meter either data transfer (gigabytes or terabytes a month) or a port speed. To compare them, the calculator spreads the monthly total evenly over an average month of 30.44 days: 1 Mbps sustained day and night moves about 329 GB a month, and 1 TB a month averages about 3 Mbps. Real traffic has peaks several times the average, which is why ports are sized for the peak. Providers that bill by the 95th percentile drop the busiest 5% of five-minute samples before taking the highest. All of this runs in your browser.