Buy a drive labeled 1 TB, plug it in, and your computer reports something noticeably smaller. That's not a manufacturing shortfall or a scam — it's two entirely different, both technically correct, definitions of what a kilobyte actually is.
The Decimal vs. Binary Standard
The decimal standard — the one storage manufacturers use on product labels — defines 1 KB as exactly 1,000 bytes, 1 MB as 1,000 KB, and so on, following the same base-10 pattern as every other metric prefix (a kilometer is 1,000 meters, after all). The binary standard, which is how most operating systems and file browsers actually calculate the sizes they display, instead defines 1 KiB as 1,024 bytes, because computers work natively in powers of two. Same prefix family, same general idea, genuinely different numbers.
Why Your Hard Drive "Loses" Storage
This is exactly the decimal-vs-binary gap in action. A drive advertised as 1 TB is sized using the decimal definition — 1,000,000,000,000 bytes. But an operating system reporting that same drive's capacity using the binary standard divides by 1,024 at every step instead of 1,000, and 1,000,000,000,000 bytes works out to roughly 931 GiB under that binary math. Nothing was actually lost — the same number of bytes is present either way — it's purely a difference in which counting system is doing the reporting.
Bits vs. Bytes: Why Speed Math Feels Off
A byte is made up of 8 bits. Internet connection speeds are conventionally advertised in bits per second (like 100 Mbps), while file sizes on your computer are conventionally shown in bytes. That mismatch in units is why a "100 Mbps" connection downloads at roughly 12.5 megabytes per second rather than 100 — dividing by 8 to convert from bits to bytes, not a sign that the connection is somehow underperforming its advertised speed.
Which Standard Actually Gets Used Where
Different platforms and contexts have made different choices about which standard to display, and not always consistently even within the same ecosystem. This is part of why the exact same physical file or drive can show a noticeably different number depending on which operating system's file browser, download manager, or command-line tool you happen to be checking it with — worth keeping in mind any time file sizes from two different sources don't quite line up.
Convert File Sizes Instantly
Convert between bits, bytes, KB, KiB, MB, MiB, GB, GiB, TB, and TiB using both standards side by side with our free File Size Converter.
FAQ
What's the difference between the decimal and binary standards? The decimal standard (used by storage manufacturers) defines 1 KB as 1,000 bytes, 1 MB as 1,000 KB, and so on. The binary standard (how operating systems and file browsers usually calculate size) defines 1 KiB as 1,024 bytes — the same prefixes, but a meaningfully different number.
Why does my hard drive show less storage than advertised? This is exactly the decimal-vs-binary difference — a drive advertised as 1 TB (1,000,000,000,000 bytes, the decimal definition) shows up as roughly 931 GiB in an operating system that reports size using the binary (1,024-based) standard.
What's the difference between a bit and a byte? A byte is 8 bits. Internet speeds are usually advertised in bits per second (like Mbps), while file sizes are usually shown in bytes — which is why a "100 Mbps" connection downloads at roughly 12.5 megabytes per second, not 100.
Why do KB and KiB use the same abbreviation in casual conversation? Mostly historical habit — the binary-based meaning of "KB" predates the formal KiB naming convention that was introduced specifically to distinguish it from the decimal definition, and many operating systems and casual conversations never fully switched over to the more precise KiB/MiB/GiB terms.