Understanding Data Amounts and Speeds
Why your internet plan is advertised in Mbit/s, but the download bar shows MB/s, and what that has to do with how fast it feels.
Last updated: September 23, 2026
How data amounts are measured
Byte, kilobyte, megabyte
1 byte8 bits, the smallest meaningful unit of storage1 kilobyte (KB)About 1,000 bytes1 megabyte (MB)About 1,000 kilobytes, a song is about 3 to 5 MB1 gigabyte (GB)About 1,000 megabytes, a movie is about 2 to 8 GB1 terabyte (TB)About 1,000 gigabytes, a typical external hard drive sizeCapital B vs. lowercase b
The letter case decides between bit or byte, an often overlooked but important difference.
MBMegabyte, capital B, used for file sizes and storageMbit or MbMegabit, lowercase b, used for internet speeds1 byte = 8 bitsThe conversion between the two unitsMbit/s vs. MB/s
Internet providers advertise in Mbit/s, but your browser or download manager usually shows MB/s.
The conversion
Since 1 byte consists of 8 bits, you divide the advertised Mbit/s number by 8 to get the approximate MB/s download speed.
Example
A 100 Mbit/s connection downloads at roughly 12.5 MB/s at most, not at 100 MB/s. At first glance this looks like a mistake by the provider, but it's simply a unit conversion.
Why it's set up this way
Networking has historically measured speed in bits per second, because data is transmitted serially, bit by bit, over a line. Storage, on the other hand, is traditionally measured in bytes.
Typical download times
Rough estimates at an assumed constant speed of 50 Mbit/s, about 6.25 MB/s.
Example calculations
A song, 5 MBAbout 1 secondA high resolution photo, 10 MBAbout 2 secondsA game update, 5 GBAbout 13 minutesA movie in good quality, 8 GBAbout 21 minutes