Kilo (symbol: k) is a prefix in the SI system denoting 10³ or 1,000. For example:

• kilogram is 1000 grams
• kilometre is 1000 metres
• kilowatt is 1000 watts
• kilojoule is 1000 joules

Adopted in 1795, it comes from the Greek χίλιοι, meaning thousand.

"Kilo" is often used by itself as an abbreviation for "kilogram". Also, technical people often use the term "k", pronounced like the letter, to refer to a thousand of something, especially units of money or population. The kilometre, on the other hand, is often abbreviated to "klick" in American, especially military usage.

Kilo is also the letter K in the NATO phonetic alphabet
Kilo class is a type of naval submarine made in Russia.

Use in computing

In computing, kilo does not always exactly denote 1000 but is usually equivalent to 1024 (2¹⁰), most often when denoting storage. For example, a kilobyte is 1024 bytes, not 1000 bytes. One prominent exception is the field of commodity hard drive manufacturing, where the smaller value is used in advertising and technical specifications. Additionally, kilo and mega often have their traditional SI meanings when referring to rates of data transfer. For instance, 56 kilobits per second is 56,000 bits per second, not 57,344 bits per second.

A common (but erroneous) convention is to use k for 1000 and K for 1024. The prefix kibi for "1024" has been introduced, but has not gained much popularity.

SI prefixes

10n	Prefix	Symbol	Short scale	Long scale Name	Decimal Equivalent
1024	yotta	Y	Septillion	Quadrillion	1 000 000 000 000 000 000 000 000
1021	zetta	Z	Sextillion	Trilliard (thousand trillion)	1 000 000 000 000 000 000 000
1018	exa	E	Quintillion	Trillion	1 000 000 000 000 000 000
1015	peta	P	Quadrillion	Billiard (thousand billion)	1 000 000 000 000 000
1012	tera	T	Trillion	Billion	1 000 000 000 000
109	giga	G	Billion	Milliard (thousand million)	1 000 000 000
106	mega	M	Million		1 000 000
103	kilo	k	Thousand		1 000
102	hecto	h	Hundred		100
101	deca, deka	da	Ten		10
10−1	deci	d	Tenth		0.1
10−2	centi	c	Hundredth		0.01
10−3	milli	m	Thousandth		0.001
10−6	micro	µ	Millionth		0.000 001
10−9	nano	n	Billionth	Milliardth	0.000 000 001
10−12	pico	p	Trillionth	Billionth	0.000 000 000 001
10−15	femto	f	Quadrillionth	Billiardth	0.000 000 000 000 001
10−18	atto	a	Quintillionth	Trillionth	0.000 000 000 000 000 001
10−21	zepto	z	Sextillionth	Trilliardth	0.000 000 000 000 000 000 001
10−24	yocto	y	Septillionth	Quadrillionth	0.000 000 000 000 000 000 000 001
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ca:Kilo da:Kilo de:Kilo el:Κιλό es:Kilo fr:Kilo pl:kilo he:קילו sl:kilo uk:Кіло fi:Kilo