How to use this calculator
Enter file size and its unit, connection speed and its unit, and the fraction of that speed available to the transfer. Use 100% for the ideal lower-bound time.
The math behind it
Seconds = file bytes × 8 ÷ usable bits per second Usable bits per second = connection rate × usable percentage ÷ 100
A worked example
A 1 GB file contains 1,000,000,000 bytes. At 100 Mbps and 100% usable speed, the ideal download takes 80 seconds.
Assumptions & precision
MB/GB/TB use powers of 1,000; MiB/GiB/TiB use powers of 1,024. A byte is 8 bits. Mbps is megabits per second; MB/s is megabytes per second. No automatic congestion, latency or protocol model; adjust usable speed yourself. Duration rounds to a second; seconds detail retains up to 6 decimals. Zero-sized files take zero time; speed and usable percentage must be positive. Converted bytes and seconds are limited to 10¹⁵.
A common question
Why is my download slower than this estimate?
Advertised line speed may exceed what the server, Wi-Fi and network path can sustain. Lower the usable percentage to model the effective rate.