Why 1KB Isn't Always 1,000 Bytes: Decimal vs. Binary Storage Units

This is one of the most persistently confusing unit conversions in computing, because two different standards have coexisted for decades — and almost nothing tells you which one it's using.

The Two Systems

Decimal (SI): 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes — used by storage manufacturers (hard drives, SSDs) and network speeds.

Binary (IEC): 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes — used by operating systems reporting file sizes and RAM.

Why This Matters Practically

It's the reason a "1TB" hard drive shows up as roughly 931GB in Windows File Explorer. The drive manufacturer used decimal (1TB = 1,000,000,000,000 bytes); Windows reports in binary (dividing by 1,024 repeatedly). Nothing is missing — it's two different definitions of the same word.

What Our Converter Handles

Bit ↔ Byte conversions (8 bits = 1 byte, always, no ambiguity there); Our converter works in binary units only: 1 KB is 1,024 bytes, and each larger step multiplies by 1,024 again.; and network speed conversions (Mbps vs MB/s — a very common mix-up, since network speeds are measured in bits, file sizes in bytes).

Units the Converter Covers

The converter handles bits, bytes, kilobytes (KB), megabytes (MB), gigabytes (GB), terabytes (TB) and petabytes (PB). A bit is one-eighth of a byte, so 1 bit equals 0.125 bytes. Results show up to six decimal places, with trailing zeros removed.

Why a 256 GB Drive Shows 238 GB

Buy a drive labelled 256 GB, install it, and your computer may report about 238 GB. A 512 GB drive may show about 476 GB. The drive has not been shortchanged. The two numbers use different units.

The math behind the gap

• Drive makers count in powers of 1,000. One GB is 1,000,000,000 bytes.
• Windows and most software count in powers of 1,024. One GB is 1,073,741,824 bytes.
• 256 GB is 256,000,000,000 bytes. Divided by 1,073,741,824, that is about 238.4, which shows as 238 GB.
• 512 GB is 512,000,000,000 bytes. Divided by 1,073,741,824, that is about 476.8, which shows as 476 GB.

Each computer GB is about 7.4% bigger than a box GB, so the same bytes produce a number about 6.9% smaller. For a quick check, divide the label by 1.074. Formatting also reserves a little space for the file system and system files, so the figure can be slightly lower again.

Windows and most software show the binary figure, such as 238 GB. Drive labels and box specs use the decimal figure, such as 256 GB.

Our converter works in binary units only, so it cannot turn 256 GB into 238 GB. To match a box label, enter 238.4 GB. The converter then shows the same number of bytes as the 256 GB label, about 256 billion.

Common Mistake: Confusing Mbps with MB/s

Mbps (megabits per second) is used for internet speed. MB/s (megabytes per second) is used for file transfer/download size. Divide Mbps by 8 to estimate real-world MB/s — a "100 Mbps" connection tops out around 12.5 MB/s, not 100 MB/s.