This bandwidth calculator estimates how long a file transfer or download takes at a given connection speed, and converts between data sizes and rates. It clears up the confusion between bits and bytes that makes real downloads feel slower than the advertised speed.
Bits, bytes and transfer time
Connection speeds are quoted in bits per second (Mbps, Gbps) but file sizes are in bytes (MB, GB), and there are eight bits to a byte. That factor of eight is why a '100 Mbps' line downloads a file at only about 12.5 megabytes per second at best. Transfer time is simply file size divided by speed, once both are in matching units, and the calculator handles the conversion so you do not have to.
Real transfers are slower than the theoretical figure because of protocol overhead, network congestion, server limits, and Wi-Fi losses. A realistic estimate applies an efficiency factor — often 80–90% of the headline rate — which the calculator can include so the prediction matches experience.
Planning around it
Estimating transfer time helps you decide whether a backup will finish overnight, how long a large upload ties up a connection, or whether a faster plan is worth it. Because time scales directly with size and inversely with speed, doubling the speed halves the time, and doubling the file doubles it.
Downloading a 2 GB file on a 100 Mbps connection.
- Convert size to bits: 2 GB × 8 = 16 gigabits = 16,000 megabits.
- Time = 16,000 Mb ÷ 100 Mbps = 160 seconds (ideal).
- Apply ~85% efficiency: roughly 190 seconds in practice.
About 160 seconds at best, closer to ~3 minutes once real-world overhead is included.
