Download Speed and Download Time Explained

The basic download time formula

Download time is calculated by dividing the amount of data being transferred by the transfer rate. Both values must use compatible units.

Mbps vs MB/s

Internet connections are commonly advertised in megabits per second, written Mbps. File sizes and application transfer rates are often shown in megabytes, written MB or MB/s. A byte contains eight bits.

Example: 100 Mbps connection

A 100 Mbps connection has a theoretical maximum transfer rate of 12.5 MB/s before accounting for protocol overhead, network congestion, server limits and other real-world factors.

Example download time

If a 1,000 MB file could be transferred continuously at 12.5 MB/s, the theoretical transfer time would be about 80 seconds.

Why actual downloads can take longer

• Wi-Fi signal quality can reduce throughput.
• The remote server may limit transfer speed.
• Other devices can share available bandwidth.
• Network congestion can change speed during a download.
• Protocol and connection overhead reduce usable throughput.
• Storage or device performance can occasionally become a bottleneck.

Internet speed vs download speed

An internet plan rated at a certain Mbps does not guarantee every download will reach that speed. The end-to-end transfer is limited by the slowest relevant part of the connection.