Mbps vs MBps: The Bandwidth Confusion Explained
You pay for 100 Mbps, the download shows 12 MB per second, and nothing is wrong. The difference is one letter of case and a factor of eight. The Bandwidth Converter moves between the two.
The one letter
A lowercase b is a bit. A capital B is a byte. A byte is eight bits.
Internet speeds are sold in bits per second, because the number is eight times larger and therefore more attractive. File sizes and download managers work in bytes per second, because that is how storage is measured.
So divide your connection speed by eight to get the download speed you will see. A 100 Mbps line gives about 12.5 MB/s. A 1 Gbps line gives about 125 MB/s. An old 8 Mbps line gives 1 MB/s, which is why that number was the threshold where the web stopped feeling slow.
This is not a trick anyone invented recently - telecoms has measured in bits since the telegraph, and storage has measured in bytes since there were bytes. But the two conventions meeting in the same progress bar is why the question keeps being asked.
Why you never get the full number
Even after dividing by eight, the real figure is lower, and the reasons are legitimate.
Protocol overhead is the main one. Every packet carries addressing and error-checking information alongside your data, which costs roughly five to ten per cent of the raw capacity before anything else happens.
The slowest link decides. Your connection is only as fast as the narrowest point between you and the server, which may be the server, or your wifi, or something in between. A gigabit line reading a file from an overloaded host will not reach gigabit.
Wifi is shared and lossy. The figure on the router's box is a theoretical maximum under perfect conditions, and real throughput is often half of it. A cable eliminates the question entirely, which is worth remembering before blaming the provider.
Storage conventions make it worse
Download managers may also use the binary definition of a megabyte - 1,048,576 bytes rather than a million - adding another few per cent of apparent discrepancy. The Data Storage Converter covers that side of it, which is the same ambiguity that makes a 1 TB drive show up as 931 GB.
Common questions
What speed do I actually need?
HD streaming wants about 5 Mbps per stream, 4K about 25. Video calls want 2 to 4 Mbps up. Most households are limited by how many streams run at once rather than by any single one.
Why is my upload so much slower?
Most domestic connections are asymmetric by design, on the assumption that people download more than they upload. It matters for video calls and backups.
Does a faster line make web pages load quicker?
Up to a point, then latency matters more than bandwidth. Past about 50 Mbps, the delay in each request dominates.
How do I convert Mbps to MB/s?
Divide by eight. Then expect ten per cent less in practice.
Got a speed figure to make sense of?