Data Storage Converter
Convert between bytes, kilobytes and kibibytes, showing decimal and binary units side by side.
Processed on your device — no upload
Bits
Bytes
Decimal — powers of 1000
Binary — powers of 1024
How to use it
- Type the size you have.
- Choose its unit — note whether it is decimal or binary.
- Read both families of units at once.
How it works
There are two families of size units and they use different bases, which is the single most confusing thing in computing measurement and the reason this page exists.
Decimal units go in powers of 1,000. A kilobyte is 1,000 bytes, a megabyte 1,000,000, a gigabyte a billion. This follows the SI prefixes used everywhere else in science, and it is what drive manufacturers, network providers and file managers on macOS use.
Binary units go in powers of 1,024. A kibibyte is 1,024 bytes, a mebibyte 1,048,576, a gibibyte 1,073,741,824. Computers address memory in powers of two, so these are the natural sizes internally — and they are what Windows shows, even though Windows labels them GB.
That mislabelling is the whole problem. Windows displays gibibytes and calls them gigabytes. The correct names — kibibyte, mebibyte, gibibyte, with the symbols KiB, MiB, GiB — were standardised by the IEC in 1998 and are still rarely used outside technical documentation.
The gap widens at every step: 2.4% at kilo, 4.9% at mega, 7.4% at giga, 10% at tera. That is why the discrepancy on a large drive feels like a rounding error at first and looks like theft by the time you reach terabytes.
A worked example
You buy a drive advertised as 1 TB. Windows shows 931 GB. Nothing is missing and nobody lied.
Type 1, choose terabyte. The result reads 0.909 TiB, or 931.32 GiB. The manufacturer sold you exactly 1,000,000,000,000 bytes, which is one terabyte by the decimal definition. Windows divides that by 1,024 three times and displays 931 — while writing “GB” next to it.
Both numbers describe the identical quantity of storage. One is labelled correctly and the other is not.
The same arithmetic explains internet speeds, with an extra trap. A “100 Mbps” connection is 100 megabits per second, not megabytes. Type 100, choose bit, and the result is 12.5 bytes — so 100 Mbps is 12.5 MB/s at best. A 1 GB file takes at least 80 seconds, not 10. The lowercase b for bits and uppercase B for bytes is a factor of eight hiding in a single letter.
One place the two systems agree: RAM is always sold and measured in binary units, because memory addressing genuinely works in powers of two. A “16 GB” memory module really is 16 GiB — 17.18 billion bytes.
If you are trying to get a file under an upload limit, compressing it is more useful than converting its size.
Questions
How do I convert MB to GB?
Type the megabytes and read the gigabytes in both systems at once. A hard drive is sold in decimal units while the operating system reports binary ones, which is where the missing space goes.
Does this work for bandwidth and file size?
Yes, but watch the unit: bandwidth is usually quoted in bits per second and a file size in bytes. Eight bits to a byte means a 100 Mbps line delivers about 12.5 MB each second.
Why does my 1 TB drive show as 931 GB?
The manufacturer sells a trillion bytes, which is 1 TB in decimal units. Windows divides by 1,024 three times, giving 931 gibibytes, and labels the result GB. Both describe the same storage; one label is wrong.
What is the difference between MB and MiB?
A megabyte is 1,000,000 bytes. A mebibyte is 1,048,576 bytes — about 4.9% more. The gap grows at every step, reaching 10% at terabytes.
Which is correct?
Both, for their own definitions. MB should mean a million bytes and MiB 1,048,576, per the IEC standard. The confusion comes from software that shows MiB and writes MB.
Why is my 100 Mbps connection only downloading at 12 MB/s?
Because Mbps is megabits and MB/s is megabytes, and there are eight bits in a byte. 100 Mbps is 12.5 MB/s at the theoretical maximum. That is your connection working correctly.
Which units does RAM use?
Binary, always. A 16 GB memory module is genuinely 16 GiB — 17,179,869,184 bytes — because memory addressing works in powers of two.
Which does macOS use?
Decimal, since OS X 10.6. A drive that shows 931 GB on Windows shows 1 TB on a Mac. Same drive, different arithmetic.
Is anything uploaded?
No. The conversion runs in your browser.
Why are the names kibibyte and mebibyte so awkward?
They were coined by the IEC in 1998 from "kilo binary" and "mega binary" to end exactly this ambiguity. They are precise and they never caught on outside technical writing.
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