Yotta-

Yotta is the largest unit prefix in the International System of Units (SI) denoting a factor of 10²⁴ or 1000000000000000000000000. It has the unit symbol Y.

The prefix name is derived from the Greek ὀκτώ (októ), meaning eight, because it is equal to 1000⁸. It was added to the SI in 1991.^[1]

Before the official adoption of the yotta prefix, the multiple was also known as otta.

Usage examples:

The mass of the Earth is 5973.6 Yg (or 5.9736 Zt).^[2]^[3]
The total power output of the Sun is approximately 385 YW. ^[4]
The above two examples, as written, make it plain to the eye that they don't make sense together, as it means that the Sun, a fusion object that is some 300,000 times more massive than the Earth, in its entirety only produces less than 20 Watts of output per gram that the Earth weighs (5973.6 Yg / 385 YW as above). This ridiculous result shows the power of using the Yotto prefix, so that the error is easily spotted.
The known universe is estimated to be 880 Ym in diameter.^[5]

SI prefixes
Prefix	Symbol	1000^m	10ⁿ	Decimal	Short scale	Long scale	Scientific notation	Since^{[n 1]}
yotta	Y	1000⁸	10²⁴	1000000000000000000000000	Septillion	Quadrillion	1E24	1991
zetta	Z	1000⁷	10²¹	1000000000000000000000	Sextillion	Trilliard	1E21	1991
exa	E	1000⁶	10¹⁸	1000000000000000000	Quintillion	Trillion	1E18	1975
peta	P	1000⁵	10¹⁵	1000000000000000	Quadrillion	Billiard	1E15	1975
tera	T	1000⁴	10¹²	1000000000000	Trillion	Billion	1E12	1960
giga	G	1000³	10⁹	1000000000	Billion	Milliard	1E9	1960
mega	M	1000²	10⁶	1000000	Million		1E6	1960
kilo	k	1000¹	10³	1000	Thousand		1E3	1795
hecto	h	1000^2/3	10²	100	Hundred		1E2	1795
deca	da	1000^1/3	10¹	10	Ten		1E1	1795
		1000⁰	10⁰	1	One		–	–
deci	d	1000^−1/3	10⁻¹	0.1	Tenth		1E-1	1795
centi	c	1000^−2/3	10⁻²	0.01	Hundredth		1E-2	1795
milli	m	1000⁻¹	10⁻³	0.001	Thousandth		1E-3	1795
micro	μ	1000⁻²	10⁻⁶	0.000001	Millionth		1E-6	1960
nano	n	1000⁻³	10⁻⁹	0.000000001	Billionth	Milliardth	1E-9	1960
pico	p	1000⁻⁴	10⁻¹²	0.000000000001	Trillionth	Billionth	1E-12	1960
femto	f	1000⁻⁵	10⁻¹⁵	0.000000000000001	Quadrillionth	Billiardth	1E-15	1964
atto	a	1000⁻⁶	10⁻¹⁸	0.000000000000000001	Quintillionth	Trillionth	1E-18	1964
zepto	z	1000⁻⁷	10⁻²¹	0.000000000000000000001	Sextillionth	Trilliardth	1E-21	1991
yocto	y	1000⁻⁸	10⁻²⁴	0.000000000000000000000001	Septillionth	Quadrillionth	1E-24	1991
^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.

References