In short: Providers sell megabits; your browser downloads megabytes. That factor of 8 is why a 100 Mbps connection never downloads at 100 megabytes per second, and why everyone's mental estimate is off by almost an order of magnitude.
Updated August 28, 2026, after a fresh review, with updated visuals and links.
Enter file size and connection speed; the tool converts everything honestly and tells you the wait, from a 2 GB game update to a 4 TB backup restore.
Megabits vs megabytes, finally clear
Internet speed is measured in megabits per second (Mbps); file size in megabytes (MB). One byte equals eight bits, so 100 Mbps moves 12.5 MB per second. The calculator shows the converted speed so the trick is visible.
Example: a 10 GB game at 100 Mbps takes about 13 minutes 39 seconds at perfect efficiency. At 25 Mbps the same file needs about 55 minutes. TB-scale restores take days, not hours: 4 TB at 100 Mbps is roughly 3 days 21 hours.
Real transfers run 10-20% under theory thanks to protocol overhead, server limits, and Wi-Fi loss. The note under the result adds that correction so planned updates do not collide with your meeting.
Worth remembering
- Test your real speed with the speed-test tool on this site before big downloads; the number on the bill is a ceiling, not an average.
- Wired Ethernet downloads measurably faster than Wi-Fi on the same plan, mainly by removing radio retransmissions.
Frequently asked
Why does my download start fast then slow down?
Many networks burst for the first seconds before throttling to sustained rates, and some servers cap per-connection speed regardless of your plan. The sustained number is the one this calculator wants.
Does upload time use the same math?
Yes, but the speed differs: most home plans are asymmetric, with upload a fraction of download. Run a speed test and use the upload figure for sending files.
Find every related tool in our Online Calculators: Every Free Tool index.
