Practical guide
Calculate file transfer time from bandwidth
Use file size, link speed, and efficiency to estimate transfer time, with a 10 GB over 100 Mbps worked example and unit checks.
Updated
Transfer time is file size in bits divided by effective throughput in bits per second. Protocol overhead, congestion, storage speed, server limits, and Wi-Fi conditions mean effective throughput is normally below the advertised link rate.
Formula and variables
seconds = file size in bytes × 8 ÷ (link bits/second × efficiency)
File size is the input payload. Link speed is the nominal bandwidth. Efficiency is the measured or assumed fraction of that bandwidth available to the transfer.
Worked example
Input: 10 decimal GB, 100 Mbps, and 90% efficiency. The file contains 80,000 megabits and the effective link rate is 90 Mbps. Output: 80,000 ÷ 90 = 888.89 seconds, about 14 minutes 49 seconds.
The most common error is reading Mbps as MB/s. One byte contains eight bits, so 100 Mbps is at most 12.5 MB/s before overhead. Use the bandwidth transfer time calculator for your inputs. On long-latency paths, the bandwidth-delay product calculator estimates the data that must remain in flight to fill the link.