Data Storage Converter
Convert digital data sizes between bits, bytes, and both decimal (kB, MB, GB, TB) and binary (KiB, MiB, GiB, TiB) units.
Two Different Kilobytes
Ask ten people how many bytes are in a kilobyte and you will get two different answers — 1 000 or 1 024 — and both sides will be right, depending on context. This ambiguity has caused real-world confusion for decades: a "500 GB" hard drive shows up as about 465 GB in Windows, a "128 GB" iPhone holds less than its label promises, and ISPs advertise speeds in megabits while your download manager counts megabytes.
The root cause is that storage hardware manufacturers adopted decimal (powers of 10) prefixes while software engineers used binary (powers of 2) addresses. The International Electrotechnical Commission (IEC) resolved this in 1998 by defining distinct binary prefixes — kibi (Ki), mebi (Mi), gibi (Gi), and so on — so that 1 KiB unambiguously means 1 024 bytes, and 1 kB unambiguously means 1 000 bytes.
The Decimal (SI) Scale
The SI system defines storage prefixes the same way it defines any physical quantity: by powers of 1 000.
| Unit | Symbol | Bytes |
|---|---|---|
| Kilobyte | kB | 10³ = 1 000 |
| Megabyte | MB | 10⁶ = 1 000 000 |
| Gigabyte | GB | 10⁹ = 1 000 000 000 |
| Terabyte | TB | 10¹² = 1 000 000 000 000 |
| Petabyte | PB | 10¹⁵ = 1 000 000 000 000 000 |
Hard drive and SSD manufacturers, USB drive makers, and memory card vendors all label capacity using these decimal values because they result in larger-sounding numbers. A "1 TB" drive contains exactly 1 000 000 000 000 bytes.
The Binary (IEC) Scale
Computer memory and operating system address spaces work in powers of 2. The IEC binary prefixes capture this exactly.
| Unit | Symbol | Bytes |
|---|---|---|
| Kibibyte | KiB | 2¹⁰ = 1 024 |
| Mebibyte | MiB | 2²⁰ = 1 048 576 |
| Gibibyte | GiB | 2³⁰ = 1 073 741 824 |
| Tebibyte | TiB | 2⁴⁰ = 1 099 511 627 776 |
| Pebibyte | PiB | 2⁵⁰ = 1 125 899 906 842 624 |
Windows, Linux, and macOS historically reported file sizes using binary math but labelled them "KB", "MB", "GB". Modern Linux and macOS have largely switched to SI labels; Windows still uses binary values with "GB" labels by default.
Bits vs. Bytes
Network speeds are measured in bits per second, not bytes. This is a deliberate industry convention: quoting speeds in bits produces a number eight times larger, which looks more impressive in marketing.
- Your home broadband is advertised in Mbps (megabits per second).
- Your download manager shows progress in MB/s (megabytes per second).
- To convert: divide Mbps by 8 to get MB/s.
A 100 Mbps connection can theoretically download at 12.5 MB/s. In practice, protocol overhead reduces this further.
Why the Gap Between Advertised and Actual Storage
The conversion factor compounds across prefix steps. At the gigabyte level, the difference is about 7 %; at the terabyte level it is about 9 %.
| Advertised | Bytes | Shown in Windows (GiB) |
|---|---|---|
| 256 GB SSD | 256 000 000 000 | ≈ 238 GiB |
| 1 TB HDD | 1 000 000 000 000 | ≈ 931 GiB |
| 4 TB HDD | 4 000 000 000 000 | ≈ 3 725 GiB |
The bytes are all there — the discrepancy is entirely a labelling convention, not missing data.
RAM Is Different
RAM capacity is specified by manufacturers using binary quantities (1 GB of RAM = 1 073 741 824 bytes), but memory chips are addressed in powers of 2 by design. This means your 16 GB RAM stick genuinely holds 16 GiB — unlike a hard drive marketed as "16 GB" which holds only 16 000 000 000 bytes.
Frequently Asked Questions (FAQ)
What is the difference between kB and KiB?
1 kilobyte (kB) = 1 000 bytes (decimal, SI prefix). 1 kibibyte (KiB) = 1 024 bytes (binary, IEC prefix). The IEC introduced the "kibi-", "mebi-", and "gibi-" prefixes in 1998 to resolve the ambiguity. File system tools and operating systems often use the binary definition while labelling it "KB", which causes confusion.
Why does my hard drive show less space than advertised?
Drive manufacturers use decimal prefixes (1 GB = 1 000 000 000 bytes), while Windows reports capacity using binary units (1 GB = 1 073 741 824 bytes) but labels them "GB". A 1 TB drive contains 1 000 000 000 000 bytes, which Windows shows as roughly 931 GB.
What is the difference between a bit and a byte?
1 byte = 8 bits. Bits are used for network speeds (Mbps, Gbps), while bytes measure file sizes and storage. To estimate a download time, divide the file size in megabytes by the connection speed in megabits per second, then multiply by 8.
How many bytes are in a GiB?
1 GiB (gibibyte) = 2³⁰ bytes = 1 073 741 824 bytes exactly. This is the amount that most operating systems call "1 GB" when reporting RAM or storage.
Disclaimer
Decimal prefixes (kB, MB, GB…) use powers of 1 000 per the SI standard. Binary prefixes (KiB, MiB, GiB…) use powers of 1 024 per the IEC 80000-13 standard.
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