How the time is calculated
File size is converted to bytes and the connection speed to bytes per second. A speed in megabits per second is divided by eight, because there are eight bits in a byte.
Time = size in bytes divided by throughput in bytes per second. Nothing else is modelled: no protocol overhead, no server throttling, no congestion.
Worked example
A 5 GB file at 100 Mbps takes 400 seconds, or 6 minutes 40 seconds. The throughput is 12.5 MB per second, which is the figure a download manager would show.
If the same file came down at 12.5 MB per second in a manager, that is the same speed; the two units describe one connection.
Why real downloads are slower
Headline speeds are the best case on a quiet line. Protocol overhead, the server's upload limit, Wi-Fi contention and peering all reduce the throughput you see.
A plan sold as 100 Mbps rarely delivers 12.5 MB per second for long. Enter what your own transfers actually achieve.
Limits of this calculator
It assumes a constant throughput for the whole transfer. It does not model TCP slow start, congestion, parallel connections or a cap applied after a data allowance is used.
It is arithmetic, not a speed test. For unit conversion alone, use the data calculator.
For conversions between decimal and binary units, use the data calculator.
Inputs for the download time calculator
File size
The size of the download, in the unit you select below.
Size unit
Decimal MB and GB, or binary MiB and GiB. Operating systems often report binary.
Connection speed
The throughput you actually get, not the advertised plan speed.
Speed unit
Broadband is sold in megabits; download managers usually show megabytes.
CALCULATOR QUESTIONS
Download time calculator questions
Why is my download slower than this estimate?
The estimate assumes a constant speed. Real transfers lose time to overhead, server limits and congestion.
Is 100 Mbps the same as 100 MB/s?
No. 100 Mbps is 12.5 MB per second, eight times smaller.
Does this include upload time?
No. It is one direction only, and upload throughput is usually lower than download.
Should I use MB or MiB?
Use whichever unit your file manager shows, and set the other field to match. Mixing them is the most common source of a wrong answer.