units(7)

💖 NAME 💖

units — decimal and binary prefixes, bestie. That's it, that's the whole page. This one's from the Miscellaneous Information Manual, section 7, and it's basically the group chat where all the prefixes hang out. ✨

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🌸 DESCRIPTION 🌸

Okay so listen — every time you type 1M or 1MiB you're using one of these, and the lore is genuinely unhinged. Let's go. 🫶

✨ Decimal prefixes ✨

The SI system of units uses prefixes that indicate powers of ten. A kilometer is 1000 meter, and a megawatt is 1000000 watt. Here's the standard lineup — read it like a roster, they all showed up 💅:

• q — quecto, 10^-30 = 0.000000000000000000000000000001
• r — ronto, 10^-27 = 0.000000000000000000000000001
• y — yocto, 10^-24 = 0.000000000000000000000001
• z — zepto, 10^-21 = 0.000000000000000000001
• a — atto, 10^-18 = 0.000000000000000001
• f — femto, 10^-15 = 0.000000000000001
• p — pico, 10^-12 = 0.000000000001
• n — nano, 10^-9 = 0.000000001
• µ — micro, 10^-6 = 0.000001
• m — milli, 10^-3 = 0.001
• c — centi, 10^-2 = 0.01
• d — deci, 10^-1 = 0.1
• da — deka, 10^ 1 = 10
• h — hecto, 10^ 2 = 100
• k — kilo, 10^ 3 = 1000
• M — mega, 10^ 6 = 1000000
• G — giga, 10^ 9 = 1000000000
• T — tera, 10^12 = 1000000000000
• P — peta, 10^15 = 1000000000000000
• E — exa, 10^18 = 1000000000000000000
• Z — zetta, 10^21 = 1000000000000000000000
• Y — yotta, 10^24 = 1000000000000000000000000
• R — ronna, 10^27 = 1000000000000000000000000000
• Q — quetta, 10^30 = 1000000000000000000000000000000

Little icon behavior moment: the symbol for micro is the Greek letter mu, often written u in an ASCII context where this Greek letter is not available. So if you see us instead of µs, that's why. iykyk. 🙈

🦋 Binary prefixes 🦋

The binary prefixes resemble the decimal ones, but have an additional 'i' (and "Ki" starts with a capital 'K'). The names are formed by taking the first syllable of the names of the decimal prefix with roughly the same size, followed by "bi" for "binary". Cute, right? It's giving ✨naming convention✨.

• Ki — kibi, 2^10 = 1024
• Mi — mebi, 2^20 = 1048576
• Gi — gibi, 2^30 = 1073741824
• Ti — tebi, 2^40 = 1099511627776
• Pi — pebi, 2^50 = 1125899906842624
• Ei — exbi, 2^60 = 1152921504606846976
• Zi — zebi, 2^70 = 1180591620717411303424
• Yi — yobi, 2^80 = 1208925819614629174706176

🎀 Discussion 🎀

Okay this is the drama section, sit down, grab a snack 🍓.

Before these binary prefixes were introduced, it was fairly common to use k=1000 and K=1024, just like b=bit, B=byte. Unfortunately, the M is capital already, and cannot be capitalized to indicate binary-ness. Like... there was nowhere left to go. Not a single letter left to raise. 💀

At first that didn't matter too much, since memory modules and disks came in sizes that were powers of two, so everyone knew that in such contexts "kilobyte" and "megabyte" meant 1024 and 1048576 bytes, respectively. What originally was a sloppy use of the prefixes "kilo" and "mega" started to become regarded as the "real true meaning" when computers were involved. Main character energy for a prefix, honestly. 👑

But then disk technology changed, and disk sizes became arbitrary numbers. After a period of uncertainty all disk manufacturers settled on the standard, namely k=1000, M=1000 k, G=1000 M. Periodt.

The situation was messy: in the 14k4 modems, k=1000; in the 1.44 MB diskettes, M=1024000; and so on. Chaos. Unhinged. No cap. 😭

In 1998 the IEC approved the standard that defines the binary prefixes given above, enabling people to be precise and unambiguous. Slay, IEC. 🔥

Thus, today, MB = 1000000 B and MiB = 1048576 B. Write that down, bestie. ✨

In the free software world programs are slowly being changed to conform. When the Linux kernel boots and says

hda: 120064896 sectors (61473 MB) w/2048KiB Cache

the MB are megabytes and the KiB are kibibytes. See? It's consistent. It ate. 🙌

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🌈 SEE ALSO 🌈

The International System of Units. 👑

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that's the whole vibe check, you're officially the prefix person at every party now, mwah 💜 This one shipped as Linux man-pages 6.20, dated 2026-02-08 — so go forth and never say "megabyte" ambiguously again, bestie. 🎀🦋