Quick example
How long does 1 GB take at 100 Mbps?
A decimal gigabyte contains 8,000 megabits. Dividing by a 100 Mbps connection gives an ideal time of 80 seconds, or 1 minute 20 seconds. Adding a simple 10% allowance gives a practical estimate of about 1 minute 28 seconds.
Avoid the common mix-up
Mbps is not the same as MB/s
Lowercase b means bits
Internet plans and speed tests usually report megabits per second as Mbps. A 100 Mbps connection moves at most 12.5 megabytes each second.
Uppercase B means bytes
File managers commonly display megabytes per second as MB/s. Because one byte is eight bits, 100 MB/s equals 800 Mbps.
Decimal and binary sizes
GB versus GiB
Decimal units use powers of 1,000: one GB is 1,000,000,000 bytes. Binary units use powers of 1,024: one GiB is 1,073,741,824 bytes. Choose the unit actually displayed by your file or storage system for the closest estimate.
Real-world performance
Why actual downloads take longer
Your advertised connection speed is a maximum, not a guarantee. Protocol overhead, network congestion, Wi-Fi signal, the remote server, storage speed, VPNs, and other devices can all extend a transfer. The practical result adds 10%, but busy or unreliable connections may take considerably longer.
Common questions
Download time FAQ
How is download time calculated?
Convert the file size to bits and divide it by the connection speed in bits per second. The answer is the ideal duration in seconds.
What is the difference between Mbps and MB/s?
Mbps measures megabits per second; MB/s measures megabytes per second. One byte equals eight bits, so 100 MB/s equals 800 Mbps.
Why is my real download slower than the estimate?
Overhead, congestion, Wi-Fi quality, server speed, storage performance, VPNs, and competing traffic can all reduce real throughput.