Download time calculator
Connections are sold in megabits, files are measured in megabytes, and there are eight bits to a byte. That factor of eight is why a 100 Mbps line moves about 12 MB a second and feels slower than the number suggests.
- In seconds
- 408.7
- Real throughput (MB/s)
- 11.50
- At the theoretical maximum
- 6 min 16 s
- File size in MB
- 4,700.0
- Downloaded per hour (GB)
- 41.40
- Maximum in 30 days (TB)
- 29.81
The formula
Bytes per second = bits per second ÷ 8 × efficiency. Time = file size in bytes ÷ bytes per second. Protocol overhead and retransmission typically cost 5% to 10%, which the efficiency factor represents.
Worked example
A 4.7 GB file on a 100 Mbps connection at 92% efficiency takes about 6 minutes 49 seconds — against 6 minutes 16 at the theoretical maximum.
How to use it
- 1Check whether your plan is quoted in megabits (Mbps) or megabytes (MB/s). The first is eight times smaller than it looks.
- 2Use a speed test result rather than the advertised figure, which is a maximum rather than a promise.
- 3Lower the efficiency to around 80% on Wi-Fi at range, or on a congested line.
Questions people ask
Why is my download slower than this?
Usually the server, not your line. Shared hosting, distant servers and per-connection throttling all cap a single download well below your connection speed.
Is upload the same calculation?
Identical arithmetic, but most domestic connections are asymmetric: upload is often a fifth to a tenth of download. Use your measured upload figure.
Last reviewed: 2026-10-20