KB vs KiB — What's the Difference?
You’ve probably seen both KB and KiB used to describe file sizes — and wondered which is correct. Here’s the short answer:
- KB = kilobyte = 1,000 bytes (decimal, base 10)
- KiB = kibibyte = 1,024 bytes (binary, base 2)
They’re not the same unit, and the difference grows as sizes get larger. DuoBolt uses KiB, MiB, and GiB throughout the app so the numbers you see always mean 1,024 bytes — the convention most operating systems actually use under the hood.
What Is a Kibibyte?
Section titled “What Is a Kibibyte?”A kibibyte (KiB) is a unit of digital information equal to 1,024 bytes. It’s part of the binary prefix system introduced by the International Electrotechnical Commission (IEC) in 1998 to resolve the long-standing ambiguity between decimal and binary interpretations of “kilobyte.”
The full set of IEC binary units:
| Prefix | Symbol | Power of 2 | Bytes |
|---|---|---|---|
| kibi | Ki | 2¹⁰ | 1,024 |
| mebi | Mi | 2²⁰ | 1,048,576 |
| gibi | Gi | 2³⁰ | 1,073,741,824 |
| tebi | Ti | 2⁴⁰ | 1,099,511,627,776 |
The “bi” in each prefix stands for “binary” — a reminder that these are base-2 measurements, unlike the metric kilo/mega/giga which use base 10.
Quick Comparison Table
Section titled “Quick Comparison Table”| Unit | Bytes | System | Where you’ll see it |
|---|---|---|---|
| 1 KB | 1,000 | SI (decimal) | Hard drives, USB sticks, network speeds, macOS Finder |
| 1 KiB | 1,024 | IEC (binary) | RAM, Windows file properties, Linux tools, DuoBolt |
| 1 MB | 1,000,000 | SI (decimal) | Storage manufacturer labels, internet speed tests |
| 1 MiB | 1,048,576 | IEC (binary) | Memory allocation, system utilities, DuoBolt |
| 1 GB | 1,000,000,000 | SI (decimal) | Drive packaging (“1 TB drive”) |
| 1 GiB | 1,073,741,824 | IEC (binary) | Actual capacity reports, DuoBolt |
Example: A file that DuoBolt reports as 100 KiB is exactly 102,400 bytes. If it were 100 KB, it would be 100,000 bytes. The difference is 2.4% — enough to matter when you’re comparing across tools.
Why the Confusion Exists
Section titled “Why the Confusion Exists”For decades, “kilobyte” meant 1,024 bytes in computing. Memory, file systems, and operating systems all used base-2 because computers work in powers of two. But storage manufacturers used 1,000 bytes so they could print larger numbers on the box — a “1 MB” hard drive had 1,000,000 bytes, not 1,048,576.
In 1998, the IEC introduced kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), and tebibyte (TiB) to end the ambiguity. The “bi” stands for “binary.”
Today, adoption is mixed:
- Windows labels sizes “KB” but actually reports KiB values in File Explorer
- macOS uses decimal units (KB = 1,000 bytes) in Finder since macOS 10.6
- Linux tools vary —
ls -lhuses KiB but prints “K”;duand many others now show “KiB” explicitly - Storage boxes always use decimal (a “2 TB” SSD is ~1.82 TiB of usable space)
Why DuoBolt Uses Binary Units
Section titled “Why DuoBolt Uses Binary Units”DuoBolt uses KiB, MiB, GiB, and TiB for two reasons:
-
Consistency with memory and OS-level reporting. File sizes, disk usage, and RAM consumption are measured in binary by the operating system. DuoBolt’s numbers match what the OS actually reports.
-
Precision. If DuoBolt says two files are both “1.00 MiB,” you can trust they’re exactly the same size down to the byte. Decimal rounding would introduce ambiguity at scale.
When you scan a drive with DuoBolt and it reports 512 GiB scanned, that’s 512 × 1,073,741,824 bytes — the real number the filesystem sees.
How the Gap Grows
Section titled “How the Gap Grows”The larger the unit, the bigger the discrepancy between decimal and binary:
| Unit | Decimal bytes | Binary bytes | Difference |
|---|---|---|---|
| Kilo | 1,000 | 1,024 | 2.4% |
| Mega | 1,000,000 | 1,048,576 | 4.9% |
| Giga | 1,000,000,000 | 1,073,741,824 | 7.4% |
| Tera | 1,000,000,000,000 | 1,099,511,627,776 | 10% |
This is why a “1 TB” drive shows up as roughly 931 GiB in DuoBolt — it hasn’t lost space, the manufacturer and the OS are just using different units.
Practical Tips
Section titled “Practical Tips”- Reading DuoBolt’s output: Ki = ×1,024, Mi = ×1,048,576, Gi = ×1,073,741,824
- Converting between them: multiply or divide by 1,024 at each step, not 1,000
- Comparing with Finder (macOS): Finder uses decimal. DuoBolt’s 100 KiB ≈ Finder’s 102.4 KB
- Comparing with File Explorer (Windows): Windows says “KB” but actually shows KiB, so DuoBolt’s numbers will match
- NAS and network storage: Many NAS systems use binary units. Check your device settings if numbers don’t match.
When in doubt, consult the byte count — bytes are unambiguous.