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Bytes, KB, MB and GB Converter

Every unit at once, with the 1000 and 1024 split made explicit.

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There are two systems. A kilobyte is 1,000 bytes and a kibibyte is 1,024. Drive manufacturers use the first, Windows reports the second, which is why a 1 TB drive shows as 931 GB.

How to use Data Size Converter

  1. Paste your sizes. One per line, with or without a unit. Plain numbers are read as bytes.
  2. Read every unit. Both the decimal and binary families are shown together.

About converting data sizes

Data sizes are quoted in two incompatible systems that share almost all of their names, which is the entire source of the confusion. The decimal system follows the SI prefixes everywhere else in measurement: kilo means a thousand, mega a million, giga a billion. The binary system uses powers of two, because memory addressing is genuinely organised that way, so its kilobyte is 1,024 bytes. For years both were called a kilobyte. The IEC introduced the binary prefixes — kibibyte, mebibyte, gibibyte — in 1998 to separate them, and adoption has been partial. Storage manufacturers use decimal units, which is also what the SI names actually mean. Windows uses binary values while labelling them with decimal names, which is the specific combination that produces the complaint. macOS and most Linux tooling report decimal, which is why the same drive shows a larger number on one machine than another. The discrepancy compounds with each step: 2.4% at kilobytes, 4.9% at megabytes, 7.4% at gigabytes and 10% at terabytes. That is why nobody notices it on a document and everybody notices it on a new drive. Bits are a separate axis and worth keeping straight. A bit is an eighth of a byte, network throughput is quoted in bits per second, and the notation differs only by the case of a single letter — so a 100 Mbps connection delivering about 12.5 MB per second is not being throttled, it is being described in the other unit.

Frequently asked questions

Why does my 1 TB drive show as 931 GB?
Because the manufacturer counted 1,000,000,000,000 bytes and Windows divides by 1,024 three times. Nothing is missing — the same number of bytes is being labelled under two different conventions, and 10^12 divided by 1024³ is 931.
What is the difference between KB and KiB?
KB is 1,000 bytes; KiB is 1,024. The binary prefixes — kibi, mebi, gibi — were introduced by the IEC in 1998 specifically to end the ambiguity. macOS and Linux mostly report decimal units, Windows reports binary values under decimal names.
Why is the gap bigger for larger units?
Because the discrepancy compounds. A kilobyte is 2.4% off, a megabyte 4.9%, a gigabyte 7.4% and a terabyte 10%. Each step multiplies the difference again, which is why the problem is barely noticeable on a file and obvious on a drive.
What about megabits?
Different unit entirely — a bit is an eighth of a byte, and network speeds are quoted in bits per second. A 100 Mbps connection downloads at about 12.5 MB per second. Bits are not accepted here, because "Mb" and "MB" differ only by case and guessing would produce answers that are wrong by a factor of eight.
Which convention should I use?
Decimal units with decimal names, or binary units with binary names — the mistake is mixing them. If you must report a binary value, call it KiB or MiB. Memory is genuinely organised in powers of two, so RAM is one place binary units are the natural fit.

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