You pay for 100 Mbps, you start a download, and your browser reports 12 MB/s. Nothing is wrong. You are simply looking at two different units, and the gap between them trips up almost everyone at some point.
Bits and bytes
A bit is the smallest unit of digital data. A byte is eight bits. Network speeds are measured in bits per second; file sizes and download managers are measured in bytes per second. That is the whole mystery.
- Mbps = megabits per second (lowercase b). Used by internet providers and speed tests.
- MB/s = megabytes per second (uppercase B). Used by browsers, download managers, and operating systems.
The divide-by-eight rule
To convert your plan speed into the download figure you will actually see, divide by eight:
- 50 Mbps ÷ 8 = about 6.25 MB/s
- 100 Mbps ÷ 8 = about 12.5 MB/s
- 300 Mbps ÷ 8 = about 37.5 MB/s
- 1000 Mbps ÷ 8 = about 125 MB/s
Our Mbps to MB/s converter does this instantly, and the download-time calculator on the same page turns it into minutes for a file of any size.
Why real downloads come in slightly under
Divide-by-eight gives the theoretical maximum. In practice you will see a little less, for reasons that are normal and unavoidable:
- Protocol overhead. Every packet carries addressing information alongside your data, typically consuming a few percent.
- The server at the other end. A download is only as fast as the slowest link, and busy servers throttle or share capacity.
- Other devices. Anything else on your network is taking a share.
- Wi-Fi. Wireless adds its own losses, often substantial ones.
Landing within about 90 percent of the theoretical figure on a wired connection is a healthy result.
A quick sanity check
If a download is running far below one eighth of your plan speed, test the connection itself with our speed test before blaming your internet. If the speed test comes back near your plan but one particular download crawls, the bottleneck is that server, not you. A very common situation with game updates and free file hosts at peak hours.
Frequently asked questions
What about Gbps?
A gigabit is 1,000 megabits. A 1 Gbps plan is 1,000 Mbps, or roughly 125 MB/s at the theoretical maximum.
Why do providers use the bigger-sounding unit?
Bits per second is the long-standing engineering convention for network links, and it happens to produce a number eight times larger. Both things are true at once.
Is a mebibyte different from a megabyte?
Slightly. Storage is sometimes counted in powers of two (1 MiB = 1,048,576 bytes) rather than powers of ten. The difference is about 5 percent and rarely matters for judging your connection.
