Data Transfer Converter

Data transfer rate measures how fast digital data moves, expressed in bits or bytes per second. This converter handles bit-based rates such as megabits per second and byte-based rates such as megabytes per second.

It is useful for understanding internet speeds and file-transfer times.

The most consequential detail on this page is a lowercase letter. Network speeds are sold in bits per second (Mbps), while file sizes and download managers report bytes per second, MB/s. A byte is eight bits, so the two differ by a factor of eight, and the abbreviations differ only in capitalisation.

A 100 Mbps connection therefore delivers at most 12.5 MB/s, and a gigabit line at most 125 MB/s. A 5 GB download over that 100 Mbps connection takes at least 400 seconds (about 6.7 minutes) under perfect conditions. Users who expect 100 MB/s conclude their connection is running at an eighth of what they paid for.

• Lowercase b is bits, uppercase B is bytes. Mbps and MB/s are not the same unit.
• Internet plans are advertised in bits per second essentially everywhere, because the number is eight times larger.
• Storage, file sizes and transfer progress are almost always in bytes.

The conversion above gives a theoretical maximum, and real transfers fall short of it for reasons that have nothing to do with the connection being mis-sold. Every packet carries protocol overhead (headers for TCP, IP and the link layer), which occupies bandwidth without carrying any of your file.

Beyond overhead, the slowest link in the path sets the ceiling. A fast connection to a slow server, a congested route, an older wireless standard or a hard drive that cannot write quickly enough will each cap the transfer well below the line rate.

• Wireless throughput is typically a fraction of its headline rate, which describes ideal conditions with no interference.
• Upload and download speeds differ on most consumer connections, and it is the upload figure that governs video calls and backups.
• Latency is a separate property from bandwidth. A high-bandwidth, high-latency link feels slow for interactive work while transferring large files perfectly well.