How to use the Download Time Calculator tool
- Enter the file size and pick the unit (MB, GB, GiB…).
- Enter the connection speed and its unit (Mbps, MB/s…).
- Choose the overhead and read the estimate. Below, enter a target time to get the required speed.
Megabits vs megabytes
Internet speeds are sold in megabits per second (Mbps), while file sizes are shown in megabytes (MB). There are 8 bits in a byte, so a 100 Mbps line moves at most 12.5 MB per second. That factor of eight is the most common reason a download seems slower than the advertised speed.
Storage adds a second trap: operating systems often count in binary units (1 GiB = 1,073,741,824 bytes) while disk makers and many apps use decimal (1 GB = 1,000,000,000 bytes). The calculator supports both.
Why real transfers are slower
- TCP/IP headers and acknowledgements take about 5 to 10 percent of the bandwidth.
- Wi-Fi, VPNs and long distances (high latency) can cost 20 percent or more.
- The other side may be slower than your line: a busy server, a cloud bucket with per-connection limits.
- Your provider’s speed is a maximum, not a guarantee, especially at peak times.
For backups and migrations, plan with the 20 percent overhead setting and add a safety margin. Moving 2 TB over a 100 Mbps line takes about two days, which often makes shipping a disk the faster option.
Privacy
Everything runs in your browser. Nothing you type is sent to our server or stored.
Frequently asked questions
How long does it take to download 1 GB at 100 Mbps?
About 80 seconds in theory and roughly 90 seconds with typical overhead.
How do I convert Mbps to MB/s?
Divide by 8. 100 Mbps is 12.5 MB/s; 1 Gbps is 125 MB/s.
Is upload the same calculation?
Yes. Just use your upload speed, which on many home connections is much lower than download.
Does the calculator include latency?
Not directly. The overhead setting covers its typical effect on throughput.