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Data Units and SI Prefixes Cheat Sheet

Every SI prefix from quecto to quetta, the binary prefixes (KiB, MiB, GiB), how far each binary unit drifts from its decimal twin, bits versus bytes, and why a 1 TB drive shows up as 931 GiB.

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Two systems share the same abbreviations. SI (decimal) prefixes are powers of 1000: 1 kB = 1,000 bytes. Binary prefixes (IEC 80000-13) are powers of 1024 and have their own names: 1 KiB = 1,024 bytes. Drive makers and network gear use decimal; many operating systems used to show binary sizes under the decimal names, which is why capacities look smaller than advertised. Convert with the Unit Converter Hub, and see download times with the Bandwidth Calculator.

SI prefixes

Prefix Symbol Factor Power of ten
quetta Q 10^30 30
ronna R 10^27 27
yotta Y 10^24 24
zetta Z 10^21 21
exa E 10^18 18
peta P 10^15 15
tera T 10^12 12
giga G 10^9 9
mega M 10^6 6
kilo k 10^3 3
hecto h 10^2 2
deca da 10^1 1
deci d 10^-1 -1
centi c 10^-2 -2
milli m 10^-3 -3
micro µ 10^-6 -6
nano n 10^-9 -9
pico p 10^-12 -12
femto f 10^-15 -15
atto a 10^-18 -18
zepto z 10^-21 -21
yocto y 10^-24 -24
ronto r 10^-27 -27
quecto q 10^-30 -30

Binary prefixes

Prefix Symbol Bytes Larger than the decimal unit by
kibi Ki 2^10 = 1,024 2.40 %
mebi Mi 2^20 = 1,048,576 4.86 %
gibi Gi 2^30 = 1,073,741,824 7.37 %
tebi Ti 2^40 = 1,099,511,627,776 9.95 %
pebi Pi 2^50 = 1.1259 × 10^15 12.59 %
exbi Ei 2^60 = 1.1529 × 10^18 15.29 %
zebi Zi 2^70 = 1.1806 × 10^21 18.06 %
yobi Yi 2^80 = 1.2089 × 10^24 20.89 %

Bits and bytes

  • 1 byte = 8 bits. Lowercase b is bits, uppercase B is bytes: Mb is megabits, MB is megabytes.
  • Network speeds are quoted in bits per second: 100 Mbit/s is 12.5 MB/s at best.
  • Storage sizes are quoted in bytes. 1 MB is 1,000,000 bytes under SI and 1 MiB is 1,048,576 bytes.

Worked examples

  • A "1 TB" drive holds 10^12 bytes, which is 931.32 GiB (the figure a binary-reporting system shows).
  • A 1 GB file (10^9 bytes) takes 80 seconds at 100 Mbit/s, ignoring protocol overhead.
  • 1 Gbit/s equals 125 MB/s.
  • A 16 GiB memory module holds 17,179,869,184 bytes.

Try these tools

Unit Converter Hub

Convert any unit instantly.

Bandwidth Calculator

Calculate how long a file transfer will take based on file size, connection speed.

Number Base Converter

Convert integers and fractions of any size between bases 2 and 36 (binary, octal, decimal, hexadecimal, base 36 and more).

See also

  • Cheat sheet Unit Conversion Factors Cheat Sheet
    Exact conversion factors for length, mass, volume, area, speed, energy, power, pressure and temperature.
  • Cheat sheet Binary, Octal & Hex Table Cheat Sheet
    0 to 31 in decimal, binary, octal and hex, the powers of two, hand-conversion shortcuts and the Base32 alphabet.
  • Glossary Byte
    A byte is a unit of digital information made of 8 bits, able to hold 256 different values from 0 to 255.
  • Glossary Bandwidth
    Bandwidth is the maximum amount of data a connection can carry per second, usually quoted in megabits per second (Mbps).
  • Glossary Scientific notation
    Scientific notation writes a number as a coefficient between 1 and 10 times a power of ten.
  • Guide How Number Bases Work: Binary, Octal and Hex
    Place value in binary, octal and hexadecimal, converting 202 between all of them step by step, hex colours.
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