Why your 300 Mbps internet downloads at 37 MB/s

Your plan says 300 Mbps. Your download manager says you’re pulling about 37 MB per second. It looks like you’re getting an eighth of what you pay for, and every month people call their provider to complain about it. Nothing is wrong. The two numbers are measured in different units that happen to differ by a factor of eight.

Bits sell, bytes save

Internet providers measure speed in megabits per second, written Mbps with a lowercase b for bits. Files and download managers measure in megabytes, written MB with an uppercase B for bytes. There are 8 bits in a byte, so to get the best-case download rate you divide the plan speed by 8. Three hundred divided by eight is 37.5 megabytes per second, which is exactly what your download manager is showing you.

Why the marketing loves bits

Because the bit number is eight times larger. ‘300 Megabit’ reads better on the box than the same speed written as ‘37 Megabyte.’ It isn’t a lie, it’s a unit choice that happens to flatter, and since every provider does it the same way, at least the comparisons between plans stay fair. You just have to remember which unit you’re holding.

The rest of the gap is overhead

You’ll often see a little less than the divide-by-8 number, and that’s normal too. Some of the connection is spent on the plumbing that makes it work, plus Wi-Fi losses, a server that caps its own upload, and neighbors sharing the line at peak hours. Losing roughly a tenth off the theoretical best is ordinary. Our Data category converts bits to bytes exactly, so you can work out what your plan should deliver and tell the difference between normal overhead and actually being shortchanged.