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ConverterData Storage Converter
Bits and bytes up to petabytes, with a switch for whether "kilo" means 1,000 or 1,024. That single choice is the entire reason a drive's box and its properties dialog never agree.
Result
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| Unit | Value |
|---|
Why a "1 TB" drive shows up as 931 GB
Storage manufacturers have always advertised capacity in decimal — 1 terabyte means exactly 1,000,000,000,000 bytes, and has since long before operating systems existed. Operating systems, on the other hand, compute free space in binary, grouping bytes in powers of 1,024 because that is how memory addressing actually works — and then, largely for historical reasons, label the result with the same unit name the manufacturer used.
Divide the manufacturer's 1,000,000,000,000 bytes by 1,024³ (1,073,741,824) and you get 931.32. The drive is not missing anything; the two sides of the screen are counting in different bases and calling both counts "GB".
| Advertised (decimal) | Reported by the OS | Apparent "loss" |
|---|---|---|
| 500 GB | 465.66 GiB | 6.9% |
| 1 TB | 931.32 GiB | 6.9% |
| 2 TB | 1.819 TiB | 9.1% |
| 4 TB | 3.638 TiB | 9.1% |
| 8 TB | 7.276 TiB | 9.1% |
Nothing here accounts for formatting overhead, the file system's own bookkeeping, or a recovery partition — all of which take a further, genuinely real bite out of usable space on top of the counting difference above.
The gap widens every time you go up a magnitude
1,024 is only 2.4% bigger than 1,000. That sounds trivial, but the gap compounds every time you multiply by another 1,024 instead of another 1,000, because the two bases are drifting apart exponentially, not by a fixed amount.
| Magnitude | Decimal (1000ⁿ) | Binary (1024ⁿ) | Gap |
|---|---|---|---|
| Kilo / Kibi | 1,000 | 1,024 | 2.3% |
| Mega / Mebi | 1,000,000 | 1,048,576 | 4.6% |
| Giga / Gibi | 1,000,000,000 | 1,073,741,824 | 6.9% |
| Tera / Tebi | 1,000,000,000,000 | 1,099,511,627,776 | 9.1% |
| Peta / Pebi | 1,000,000,000,000,000 | 1,125,899,906,842,624 | 11.2% |
By the time you reach petabyte scale, the "same" number in the two systems has drifted apart by over 11%. There is no magnitude where the gap closes again — it only grows.
IEC prefixes exist specifically to fix this ambiguity
In 1998 the International Electrotechnical Commission standardised a separate set of names — kibi, mebi, gibi, tebi, pebi — that only ever mean powers of 1,024, so "KB" could go back to meaning strictly 1,000 without argument.
| Decimal | Binary | Value | Who uses it this way |
|---|---|---|---|
| KB — kilobyte | KiB — kibibyte | 10³ vs 2¹⁰ | Drive and SSD spec sheets are always decimal; RAM capacity and network throughput (Mbps) are decimal too |
| MB — megabyte | MiB — mebibyte | 10⁶ vs 2²⁰ | macOS Finder has reported decimal since 2009; Windows File Explorer still computes in binary but mislabels the result "MB" |
| GB — gigabyte | GiB — gibibyte | 10⁹ vs 2³⁰ | Linux tools split down the middle — df -h is binary by default, df -h --si is decimal |
| TB — terabyte | TiB — tebibyte | 10¹² vs 2⁴⁰ | The IEC names are correct and unambiguous almost nowhere they are used in consumer software |
In honest terms: almost no mainstream operating system actually writes "GiB" on screen even when that is the number it computed. The IEC prefixes solved the ambiguity on paper in 1998; the industry mostly still writes "GB" for both meanings and expects you to know which one applies from context. This converter uses the correct IEC names in its own labelling once you switch to binary mode, precisely so the two modes are never confusable with each other here.
Questions people ask
Which mode should I use to match my file manager?
Binary (1,024), almost always — that is what Windows Explorer, macOS's older Finder versions and most file browsers compute internally, even though they label the result "GB" instead of the technically correct "GiB". Use decimal only when checking a manufacturer's advertised capacity or a network speed rating.
Is a megabit the same as a megabyte?
No — a byte is 8 bits, so 1 megabyte is 8 megabits. Internet speeds are quoted in megabits per second (Mbps), which is why a "100 Mbps" connection downloads a file at roughly 12.5 MB per second, not 100.
Why does the breakdown table show a huge or tiny number?
Because you are looking at the same quantity at a magnitude a long way from where it naturally sits — 1 byte expressed in petabytes is a number with fifteen leading zeros after the decimal point. That is expected, not a bug.