Bytes to Bits Converter

bytes to bits — quick reference

The formula, worked line by line

One multiplication by eight. The value of writing it out is not the arithmetic but the unit bookkeeping, because this is the conversion people perform in their heads and then apply to the wrong one of the two numbers.

Getting into the habit of reading that letter first is worth more than any of the arithmetic below. A figure whose unit you have not checked is not yet a figure you can compare with anything.

bits = bytes x 8
bytes = bits / 8
1 MB = 1,000,000 bytes = 8,000,000 bits
seconds = bits / (bits per second)
4 GB over 100 Mbps = 32,000,000,000 / 100,000,000 = 320 s

Where the two units meet in practice

Anywhere storage touches transmission. A backup window is a file size in bytes against a link in bits. A video bitrate is bits per second against a file that will land on disk in bytes. A monthly data cap is usually stated in bytes while the meter that fills it is counting bits on a wire.

The two families of prefix, both in play

That last point is worth holding on to. When you see Mbps you can take the prefix literally. When you see MB you have to ask which divisor produced it. The bit side of this conversion is the unambiguous side.

How to use the bytes to bits converter

Eight bits to the byte, so this is a multiplication by eight. It is the simplest conversion on this shelf and the one that causes the most argument, because it sits exactly on the boundary between two industries that chose different units and never reconciled them.

Storage is sold in bytes. Bandwidth is sold in bits. A file is a number of bytes and a connection is a number of bits per second, so no download-time question can be answered until one side has been converted to the other. This page does that conversion in the direction that starts from the file.

The case of the letter b carries the entire distinction and nothing else does. Mbps is megabits per second; MBps or MB/s is megabytes per second. They are eight times apart, they are written almost identically, and the smaller-looking one is the larger quantity. Marketing material has never had a reason to make this clearer.

Once both sides are in bits the arithmetic is trivial and, more usefully, the units cancel. Bits divided by bits per second leaves seconds. That is worth doing on paper once, because it makes the sanity check obvious: if your answer has a strange unit attached, one of the two figures was in the wrong currency.

Why a byte settled on eight bits

The eight-bit byte is a convention that won, not a law of physics. Early machines used bytes of six, seven and nine bits, and some let programmers choose the width instruction by instruction. The DEC PDP-10 could address fields of any size within its 36-bit word, so a byte there was whatever you declared it to be.

The practical residue of that history is the word octet in every networking standard you will ever read. It means exactly eight bits and it cannot mean anything else, whereas byte technically depends on the machine. On any hardware you are likely to meet, the two are the same thing.

Why eight is the floor, not the answer

Converting bytes to bits gives the amount of data. It does not give the amount transmitted, because every layer of the network adds its own framing around your payload, and that framing is also made of bits that occupy the line.

A realistic figure over Ethernet and TCP is around 94 percent of the raw rate once headers and acknowledgements are counted, and less over wireless or a congested path. So a gigabit connection that tests at 940 Mbps is behaving normally, and the 12.5 MB/s figure for a 100 Mbps line is a ceiling rather than a promise.

Every bytes value, worked out

140 common bytes figures each get their own page, with the answer, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask