FileSizeCalc

MB vs MiB — Binary and Decimal Data Units Explained

MB and MiB look like a typo and behave like a six-figure accounting error at scale. The difference is 4.9% per step, and knowing which name applies to which product turns a confusing pile of numbers into a consistent picture.

Quick answer: MB (megabyte) = 1,000,000 bytes, defined by SI. MiB (mebibyte) = 1,048,576 bytes (1024²), defined by the IEC in 1998. Hardware and networks use decimal; most operating systems display binary but label it MB.

The full IEC ladder

  • kB = 1,000 B · KiB = 1,024 B
  • MB = 10⁶ B · MiB = 1024² B = 1,048,576 B
  • GB = 10⁹ B · GiB = 1024³ B = 1,073,741,824 B
  • TB = 10¹² B · TiB = 1024⁴ B = 1,099,511,627,776 B
  • PB = 10¹⁵ B · PiB = 1024⁵ B = 1,125,899,906,842,624 B

How much the gap grows

Each step adds 2.4% on top of the decimal figure, and the effects compound: one step is 2.4%, three steps (bytes to gibibytes) is 7.4%, five steps (petabytes) is 12.6%. That is why the discrepancy is invisible for small files and unmissable at drive sizes — and why comparing a 4 PB cloud bill against local binary tooling can look like an 11% accounting error.

Why the IEC bothered to define MiB

In the 1990s, disk manufacturers and software vendors argued about who was misleading consumers — the same drive was “1 GB” to one and “0.95 GB” to the other. The IEC resolved it by naming both quantities: the SI family keeps decimal powers, and a new binary family carries the -i- syllable. Adoption stayed partial: Linux and technical standards use MiB, while Windows and most consumer software still write “MB” for the binary value.

Practical rules

  • Buying storage: trust the decimal label, expect the binary display.
  • Networking: everything is decimal (Mbps, Gbps, and GB of data plans).
  • Memory and caches: RAM is binary, so a “16 GB” DIMM is 16 GiB.
  • Backups and quotas: check whether the tool counts decimal (billing) or binary (local display).
  • When precision matters, state bytes — no unit naming can distort a byte count.

Frequently Asked Questions

Is MiB bigger than MB?
Yes: 1 MiB = 1,048,576 bytes, about 4.9% larger than 1 MB = 1,000,000 bytes.
Does Windows use MiB?
It uses binary quantities (1,024-based) but labels them MB/GB, not MiB/GiB — the value is binary, the name is decimal.
Where is MiB actually used?
Linux tools, storage standards, virtualisation platforms and technical documentation; rarely on consumer packaging.
How do I remember the difference?
The -i- stands for binary: Kibi, Mebi, Gibi, Tebi — all powers of two. No -i-, no 1024.

More tools mentioned in this guide

GB to MB Converter
Convert gigabytes to megabytes with the 1024 and 1000 rules both shown
MB to GB Converter
Turn megabytes into gigabytes with both 1024 and 1000 conventions
How Many MB in a GB
The straight answer, both conventions, and why your storage disagrees
Hard Drive Capacity Calculator
Why a 1 TB drive shows 931 GB — exact usable capacity math

More guides

Why a 1 TB Drive Shows 931 GB
The decimal-versus-binary answer in plain language
How Many GB in a TB
1,000 or 1,024 — and what that means for real drives