Digital storage has a units problem. The SI prefixes kilo, mega and giga mean powers of 1,000, but computers count in powers of 2, and for decades the same names were used for both. A “gigabyte” could mean 1,000,000,000 bytes on a drive’s box or 1,073,741,824 bytes in an operating system, a 7.4% gap that grows to almost 10% at the terabyte level. The International Electrotechnical Commission solved this with separate binary prefixes — kibi, mebi, gibi, tebi — and this converter keeps the two systems strictly apart.
How to use the data storage converter
- Enter the size in Value.
- Choose its unit in From. Every option shows its exact size: decimal units say “10ⁿ bytes,” binary units say “2ⁿ bytes.”
- Choose the target unit in To.
- The tape shows the result, the total bytes and bits, and how Windows and macOS would each display that size.
- Three tables list the value in all decimal units, all binary units and all bit units.
Data storage conversion formula
Every unit is converted through bytes:
| Decimal (SI) | Bytes | Binary (IEC) | Bytes |
|---|---|---|---|
| kilobyte (kB) | 1,000 | kibibyte (KiB) | 1,024 |
| megabyte (MB) | 1,000² = 1,000,000 | mebibyte (MiB) | 1,024² = 1,048,576 |
| gigabyte (GB) | 1,000³ | gibibyte (GiB) | 1,024³ = 1,073,741,824 |
| terabyte (TB) | 1,000⁴ | tebibyte (TiB) | 1,024⁴ ≈ 1.0995 × 10¹² |
| petabyte (PB) | 1,000⁵ | pebibyte (PiB) | 1,024⁵ ≈ 1.1259 × 10¹⁵ |
A bit is the smallest unit (a 0 or 1), and 8 bits make a byte. Network speeds use decimal bit units: 1 Mbit = 1,000,000 bits = 125,000 bytes.
Worked example: a “1 TB” drive
1 TB = 1,000,000,000,000 bytes
1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB
1,000,000,000,000 ÷ 1,099,511,627,776 = 0.9095 TiB
That is why File Explorer reports about 931 GB for a 1 TB drive, while macOS, which has used decimal units since 2009, shows 1 TB. Both are correct; they are counting the same bytes in different units. A 500 GB drive likewise shows as 465.66 GB in Windows.
How big is the gap?
| Prefix level | Decimal | Binary | Binary is larger by |
|---|---|---|---|
| kilo / kibi | 10³ | 2¹⁰ | 2.4% |
| mega / mebi | 10⁶ | 2²⁰ | 4.9% |
| giga / gibi | 10⁹ | 2³⁰ | 7.4% |
| tera / tebi | 10¹² | 2⁴⁰ | 10.0% |
| peta / pebi | 10¹⁵ | 2⁵⁰ | 12.6% |
Who uses which units
- Drive and SSD makers, USB sticks, memory cards: decimal (GB, TB).
- RAM: binary in practice. A “16 GB” memory module holds 16 GiB, following a long-standing JEDEC convention.
- Windows: binary values labeled with decimal symbols (KB, MB, GB).
- macOS and iOS: decimal since Mac OS X 10.6 in 2009.
- Linux tools: vary; many show KiB/MiB/GiB explicitly, others use decimal.
- Networking and internet plans: decimal bits per second (Mbit/s, Gbit/s).
Bits, bytes and transfer speeds
Lowercase b means bits and uppercase B means bytes, so 100 Mb/s and 100 MB/s differ by a factor of 8. To estimate how long a file takes to transfer, convert its size to bits (or the line speed to bytes) first. A 4 GB movie is 32,000 Mbit, so on a 100 Mbit/s connection it needs at least 320 seconds, about five and a half minutes, before overhead. The download time calculator does this for you. To see how numbers are stored as bits, try the binary, hex and decimal converter; for SI prefixes on any other unit, see the metric prefix converter.
Frequently asked questions
Is a gigabyte 1,000 or 1,024 megabytes?
Officially, a gigabyte (GB) is 1,000 megabytes, or 10⁹ bytes. The binary unit of 1,024 mebibytes (2³⁰ bytes) is called a gibibyte (GiB). Windows still labels gibibytes as "GB," which keeps the confusion alive.
Why does my 1 TB drive show only 931 GB?
The drive holds 1,000,000,000,000 bytes, as advertised. Windows divides by 1,024³ instead of 1,000³ and reports 931.32 binary gigabytes, labeled GB. No space is missing; the two numbers measure the same bytes with different units.
How do I convert megabits to megabytes?
Divide by 8, because a byte has 8 bits. A 100 Mbit/s internet connection moves at most 12.5 MB per second, before protocol overhead.
What is the difference between kB, KB and KiB?
In SI notation kB (lowercase k) is 1,000 bytes. KiB is the binary kibibyte of 1,024 bytes. KB with a capital K is informal and usually means 1,024 bytes in memory specifications, but it is ambiguous, so check the context.