How Many MB in a Gigabyte?
1000 when you're talking about files and storage; 1024 when you're talking about RAM. Both have been in use since the start of computing — and there's a quarter-century-old international standard, largely ignored, that was meant to end the argument.
Where the two numbers came from
Computers count in binary, so memory sizes fall naturally on powers of two: 2, 4, 8, 16, 32. The closest power of two to a thousand is 1024, so early engineers borrowed the metric prefix "kilo" and quietly redefined it from 1000 to 1024 — close enough that nobody minded. As units grew, the fudge grew with them: a kilobyte is only 2.4% off, but by the gigabyte the two systems differ by 7.4%, and by the terabyte by almost 10%. Storage makers, meanwhile, stuck with the true decimal 1000, partly for correctness and partly because it makes the number on the box bigger. The ladder below shows the split at every level.
The fix that almost nobody uses
In 1998 the International Electrotechnical Commission tried to settle it for good. It minted a whole new set of binary prefixes — kibi, mebi, gibi, tebi — giving us the kibibyte (1024 bytes, KiB), mebibyte (1,048,576 bytes, MiB) and gibibyte (GiB). Under the rules a megabyte is now unambiguously a million bytes and a mebibyte is the binary one. It's a tidy solution that the technical world mostly adopted and the everyday world mostly didn't: Linux and macOS use it in places, but Windows still reports "GB" when it means GiB, and almost nobody says "gibibyte" out loud. The standard is correct, widely available, and quietly losing.
Why your RAM and your hard drive disagree on purpose
This is why the two components in the same computer use different rules. RAM is wired in powers of two — there's no practical way to build a stick of exactly 10 GB — so it's sold as 8, 16 or 32 and counted in 1024s. A hard drive or SSD has no such constraint, so it's sold in round decimal numbers and counted in 1000s. Put a "16 GB" RAM stick and a "1 TB" SSD in the same machine and they're each telling the truth in a different language. To see how that plays out as the apparent "missing" space on a drive, the GB-in-a-terabyte page has a calculator for exactly that.
Frequently asked questions
How many MB in a GB?
1000 in the decimal system used for storage and data caps, or 1024 in the binary system used for RAM and much software. Strictly the binary figure is 1 GiB = 1024 MiB; everyday usage just writes "GB".
Is it 1000 or 1024?
Both are in active use. Files, drives, and your phone plan use 1000. RAM and a lot of operating-system reporting use 1024. The official binary prefixes (KiB, MiB, GiB) were created in 1998 specifically to keep the two apart.
Why does RAM use 1024 but hard drives use 1000?
RAM is addressed in powers of two, so its capacities land naturally on 1024-based numbers — which is why you buy 8, 16 or 32 GB, not 10 or 20. Drives have no such constraint, so makers use the round decimal 1000, which also makes the headline number bigger.
What is a mebibyte (MiB)?
It's the precise name for 1,048,576 bytes — exactly 1024 kibibytes. The IEC introduced "mebi", "gibi" and friends in 1998 so a megabyte could mean 1,000,000 bytes and a mebibyte 1,048,576, with no ambiguity.
- SI / decimal: 1 GB = 10⁹ bytes = 1000 MB — used for storage, files and data plans.
- IEC 80000-13 (binary prefixes, introduced 1998): kibibyte (KiB), mebibyte (MiB, 1,048,576 bytes), gibibyte (GiB, 1024 MiB).
- The decimal/binary gap compounds: KB 2.4%, MB 4.9%, GB 7.4%, TB 10.0%, PB 12.6%.
- RAM capacities follow powers of two (8, 16, 32 GB); storage follows round decimal numbers — the reason the two count differently.
There's a perfectly good word for the 1024 version — mebibyte — and the fact you've probably never said it is the whole story.