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Atto (a) Unit Definition
Atto is a SI unit prefix in the metric system denoting a factor of 10-18 or 0.000000000000000001. It is represented by the prefix atto or the symbol a.
Overview
The unit multiple was adopted at the 12th General Conference on Weights and Measures (CGPM) in Resolution 8. It is derived from the Danish word atten, meaning eighteen.
Examples
Weight of the HIV-1 virus is about 1×10-18 kilograms (kg) or 1×10-15 grams (g), which can be written as 1 femtograms (fg) or 1000 attograms (ag).
SI Prefixes
Here is a table of the SI prefixes and some of their properties:
Name & Symbol |
Base 10 |
Decimal |
English Word |
Adoption |
|
Short Scale |
Long Scale |
||||
Quetta (Q) | 1030 |
1,000,000,000,000,000,000,000,000,000,000 |
Nonillion |
Quintillion |
2022 |
Ronna (R) | 1027 |
1,000,000,000,000,000,000,000,000,000 |
Octillion |
2022 |
|
Yotta (Y) | 1024 |
1,000,000,000,000,000,000,000,000 |
Septillion |
Quadrillion |
1991 |
Zetta (Z) | 1021 |
1,000,000,000,000,000,000,000 |
Sextillion |
Trilliard |
1991 |
Exa (E) | 1018 |
1,000,000,000,000,000,000 |
Quintillion |
Trillion |
1975 |
Peta (P) | 1015 |
1,000,000,000,000,000 |
Quadrillion |
Billiard |
1975 |
Tera (T) | 1012 |
1,000,000,000,000 |
Trillion |
Billion |
1960 |
Giga (G) | 109 |
1,000,000,000 |
Billion |
Milliard |
1960 |
Mega (M) | 106 |
1,000,000 |
Million |
1873 |
|
Kilo (k) | 103 |
1,000 |
Thousand |
1795 |
|
Hecto (h) | 102 |
100 |
Hundred |
1795 |
|
Deca (da) | 101 |
10 |
Ten |
1795 |
|
One (1) | 100 |
1 |
One |
- |
|
Deci (d) | 10-1 |
0.1 |
Tenth |
1795 |
|
Centi (c) | 10-2 |
0.01 |
Hundredth |
1795 |
|
Milli (m) | 10-3 |
0.001 |
Thousandth |
1795 |
|
Micro (µ) | 10-6 |
0.000001 |
Millionth |
1873 |
|
Nano (n) | 10-9 |
0.000000001 |
Billionth |
Milliardth |
1960 |
Pico (p) | 10-12 |
0.000000000001 |
Trillionth |
Billionth |
1960 |
Femto (f) | 10-15 |
0.000000000000001 |
Quadrillionth |
Billiardth |
1964 |
Atto (a) | 10-18 |
0.000000000000000001 |
Quintillionth |
Trillionth |
1964 |
Zepto (z) | 10-21 |
0.000000000000000000001 |
Sextillionth |
Trilliardth |
1991 |
Yocto (y) | 10-24 |
0.000000000000000000000001 |
Septillionth |
Quadrillionth |
1991 |
Ronto (r) | 10-27 |
0.000000000000000000000000001 |
Octillionth |
2022 |
|
Quecto (q) | 10-30 |
0.000000000000000000000000000001 |
Nonillionth |
Quintillionth |
2022 |
Other Prefix Unit Definitions
- Atto (a)
- Centi (c)
- Deca (da)
- Deci (d)
- Deka (da)
- Exa (E)
- Exbi (Ei)
- Femto (f)
- Gibi (Gi)
- Giga (G)
- Hecto (h)
- Kibi (Ki)
- Kilo (k)
- Mebi (Mi)
- Mega (M)
- Micro (µ)
- Milli (m)
- Nano (n)
- One (1)
- Pebi (Pi)
- Peta (P)
- Pico (p)
- Qubi (Qi)
- Quecto (q)
- Quetta (Q)
- Robi (Ri)
- Ronna (R)
- Ronto (r)
- Tebi (Ti)
- Tera (T)
- Yobi (Yi)
- Yocto (y)
- Yotta (Y)
- Zebi (Zi)
- Zepto (z)
- Zetta (Z)
Convert to Another Prefix Unit
Related Definitions
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Sources
“Atto-.” Wikipedia, Wikimedia Foundation, 9 Jan. 2020, en.wikipedia.org/wiki/Atto-.