Why the real time can differ
Connection speed tests show a moment in time. Wi-Fi quality, network congestion, other devices and the source server can reduce the speed available to one download.
Mbps and MB are different
Internet speed is normally measured in megabits per second, while file size is shown in megabytes or gigabytes. Eight bits make one byte, so the calculator converts between them.
A practical allowance
The estimate includes a small transfer overhead by default. It is still a planning figure rather than a promise, especially on mobile and shared connections.
Large 4K files
High-resolution video can be several gigabytes. Use the estimate before starting a large transfer on limited mobile data or a connection that may be interrupted.