How Many MB Are in a GB?

The short answer is 1,024 MB — but you may also have seen 1,000, and both numbers are correct depending on who is doing the counting. That single disagreement is the reason a 1 TB drive shows up as 931 GB, why a new phone has less free space than the box promised, and why two apps can report the same file at two different sizes.

This guide gives you the number you came for in the first line, then explains the 1,000-vs-1,024 split properly, walks the full ladder from bytes to terabytes, and clears up the other size confusion nobody warns you about: Mb is not MB. If you just need the arithmetic done, our MB to GB converter and GB to MB converter run entirely in your browser.

If you are checking a file size on a computer, use 1,024. If you are reading a spec sheet, a storage advertisement or a mobile data allowance, use 1,000. Our converters use the binary figure, because that is what your operating system reports back to you.

Computers address memory in powers of two. The closest power of two to a thousand is 2¹⁰, which is 1,024 — so early engineers borrowed the metric prefix "kilo" and applied it to 1,024 bytes. It was close enough, and it stuck.

The metric system, meanwhile, is strict: kilo means exactly 1,000, mega means 1,000,000, giga means 1,000,000,000. Storage manufacturers sell by the metric definition, which is both technically correct and — conveniently — makes the number on the box bigger.

In 1998 the IEC introduced separate binary prefixes to end the ambiguity: kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) and tebibyte (TiB), each a power of 1,024. They are the standards-correct way to write binary sizes. Almost nobody outside Linux uses them, so in practice you will keep seeing "GB" used for both meanings and have to work out which one from context.

Each step up is 1,024× in binary, or 1,000× in decimal. Every size is expressed in bytes, because the byte is the one unit both conventions agree on.

Notice the gap column. The two conventions differ by only 2.4% at the kilobyte, but the error compounds at every rung — by the terabyte it is nearly 10%, and at the petabyte it is over 12%. This is why nobody argues about KB and everybody argues about TB.

The same 1,024 step applies at every level. These are the conversions people look up most:

• How many KB in a MB? 1,024 KB (or 1,000 decimal) — KB to MB converter
• How many MB in a GB? 1,024 MB (or 1,000 decimal)
• How many GB in a TB? 1,024 GB (or 1,000 decimal) — TB to GB converter
• How many MB in a TB? 1,048,576 MB — that is 1,024 × 1,024
• How many bytes in a KB? 1,024 bytes
• How many bytes in a GB? 1,073,741,824 bytes

For anything not on this list, the unit converter handles the whole digital category, plus length, weight, temperature and more.

This is the single most common storage complaint, and nothing is wrong with your drive. It is the two conventions colliding.

The manufacturer sold you a terabyte using the decimal definition: 1,000,000,000,000 bytes. Your operating system then divides that by the binary gigabyte, 1,073,741,824 bytes:

1,000,000,000,000 ÷ 1,073,741,824 = 931.32

So your drive holds exactly what was advertised. It is being measured with a different ruler than the one used to sell it. The same arithmetic explains every other "missing" capacity:

One caveat: on a phone or a new laptop, some space really is gone — the operating system, recovery partition and preinstalled apps occupy real storage on top of this conversion difference. On a blank external drive, the 7.37% is the entire explanation.

We verified the terminal behaviour rather than assuming it: a file of exactly 1,048,576 bytes is reported as 1.0M by both ls -lh and du -h on macOS. If it were using the decimal megabyte it would read 1.0M only at 1,000,000 bytes.

This one costs people more confusion than the 1,000/1,024 split, because the abbreviations differ by a single capital letter.

• MB — megabyte, a measure of storage. Capital B.
• Mb or Mbps — megabit, a measure of speed. Lowercase b.

There are 8 bits in a byte, so a connection advertised at 100 Mbps delivers roughly 12.5 MB per second, not 100. Internet providers quote bits because it makes the number eight times larger.

A 50 GB game download on a 100 Mbps line therefore takes about 72 minutes at best — and that is the theoretical maximum, before real-world overhead.

Unit tables are abstract. Here is what a gigabyte actually holds, using 1 GB = 1,024 MB:

File sizes vary enormously with quality settings and codec, so treat these as orders of magnitude rather than exact counts.

Most people arrive at a size conversion because something has been rejected. Email is the usual culprit: Gmail and Yahoo cap attachments at 25 MB, Outlook.com at 20 MB, and many corporate mail servers are stricter still.

Knowing the number rarely fixes it — shrinking the file does:

1. Images — run them through Image Compressor. A 4 MB phone photo typically drops below 1 MB with no visible loss. If the dimensions are larger than they need to be, Image Resizer saves more than compression alone.
2. PDFs — PDF Compressor re-encodes embedded images, which is where nearly all the weight in an oversized PDF lives.
3. Several files at once — combine them first with PDF Merge so you are sending one attachment instead of six.

All of these run entirely in your browser. Nothing is uploaded to a server, so the file never leaves your device.

Use 1,024 when you are reading a number off a computer, and 1,000 when you are reading one off a box or a bill. The two answers differ by 7.37% at the gigabyte and by almost 10% at the terabyte, which is enough to explain every "missing storage" question ever asked and not enough to matter for anything else.

When you need the arithmetic done rather than explained, the MB to GB, GB to MB, KB to MB and TB to GB converters are one click away, and the full unit converter covers everything else.