What is MB/s?

MB/s in one line

mb/s means megabytes per second — how many megabytes of data move every second. The letters are often written lowercase (mb/s, MB/s or Mbps in loose usage), but they are not the same thing:

• MB/s (capital B) = megabytes per second = 8 Mbps. This is what download windows and drive specs use.
• Mb/s or Mbps (lowercase b) = megabits per second. This is what internet providers sell and speed tests report.

So a 500 Mbps plan tops out at 62.5 MB/s, and a download window showing 11 MB/s means you are getting about 88 Mbps. The whole difference is one letter: 1 MB/s = 8 Mbps.

MB/s × 8 = Mbps
Mbps ÷ 8 = MB/s

The definition

A megabyte is 1,000,000 bytes and a byte is 8 bits, so:

1 MB/s = 1,000,000 B/s = 8,000,000 bit/s = 8 Mbps
1 kB/s = 1,000 B/s = 8 kbps
1 GB/s = 1,000 MB/s = 8 Gbps

It is sometimes written MBps or MB/sec. The capital B is what matters: MB/s is bytes, Mbps is bits. Network speeds and plans use Mbps, explained in what is Mbps, and why one unit counts bits and the other bytes is the subject of bits vs bytes.

Where you see MB/s

• Downloads. Browsers, game launchers and download managers report how quickly the file grows on disk, in kB/s or MB/s.
• File copies. Copying to a USB stick, an external drive or a network share shows a speed in MB/s in most operating systems.
• Drive and memory card specs. Read and write speeds for SSDs, hard drives and cards are quoted in MB/s, because storage is measured in bytes.
• Cloud sync and backup apps. Many show upload progress in MB/s, even though your plan's upload is sold in Mbps.

Small rates appear as kB/s: 500 kB/s is 4 Mbps, which is why a slow download that "only" shows a few hundred kB/s may still be using a modest plan fully. The kB/s to Mbps converter covers that range.

Port and cable speeds in MB/s

Connections such as USB and Ethernet are rated in bits per second. Dividing by 8 gives the ceiling in MB/s. These are nominal signalling rates; real copies are lower because of encoding, protocol overhead and the drive at each end.

A copy is limited by the slowest part of the chain. A fast SSD on a USB 2.0 port cannot exceed 60 MB/s, and a gigabit network share cannot exceed 125 MB/s however fast the drives are. The file transfer time calculator has these connections as presets.

MB/s vs MiB/s

Some programs count in binary units: 1 MiB/s is 1,048,576 bytes per second, about 4.9% more than 1 MB/s. Some label it MiB/s; others still write "MB/s" while dividing by 1,024 × 1,024. The difference is small for a quick check but adds up in precise comparisons:

1 MB/s  = 8 Mbps
1 MiB/s = 8.388608 Mbps
117.5 MB/s ≈ 112.1 MiB/s

If a program's reading and a speed test disagree by about 5%, binary units are a likely reason.

The same applies to sizes. A file listed as "4 GB" by software that counts in binary is 4 GiB, which is 4,294,967,296 bytes. Copying it at 100 MB/s takes about 42.9 seconds, not 40. For a quick estimate the difference rarely matters; for comparing two tools, or a tool with a speed test, it can explain the whole gap.

Using MB/s to estimate time

Because file sizes and MB/s are both in bytes, time is a simple division with no factor of 8:

seconds = size in MB ÷ MB/s
10 GB at 100 MB/s = 10,000 MB ÷ 100 = 100 s

When the speed is a plan in Mbps, convert first: a 500 Mbps plan is at most 62.5 MB/s, so the same 10 GB takes at least 160 seconds. The download time calculator accepts either unit and does the conversion for you, and the MB/s to Mbps converter handles single values.

For rates in bytes of any size, from B/s to GB/s, the bytes to Mbps converter shows the Mbps equivalent and every other unit at once.