# Kappa

**Kappa** /ˈkæpə/^{[1]} (uppercase **Κ**, lowercase **κ** or cursive **ϰ**; Greek: κάππα, *káppa*) is the 10th letter of the Greek alphabet, used to represent the [k] sound in Ancient and Modern Greek. In the system of Greek numerals, *Kʹ* has a value of 20. It was derived from the Phoenician letter kaph . Letters that arose from kappa include the Roman K and Cyrillic К.

Greek proper names and placenames containing kappa are often written in English with "c" due to the Romans' transliterations into the Latin alphabet: Constantinople, Corinth, Crete. All formal modern romanizations of Greek now use the letter "k", however.^{[citation needed]}

The cursive form ϰ is generally a simple font variant of lower-case kappa, but it is encoded separately in Unicode for occasions where it is used as a separate symbol in math and science. In mathematics, the kappa curve is named after this letter; the tangents of this curve were first calculated by Isaac Barrow in the 17th century.

## Symbol

### Lowercase (κ)

- Mathematics and statistics

- In graph theory, the connectivity of a graph is given by
*κ*. - In differential geometry, the curvature of a curve is given by
*κ*. - Kappa statistics such as Cohen's kappa and Fleiss' kappa are methods for calculating inter-rater reliability.

- Physics

- In cosmology, the Einstein gravitational constant is denoted by
*κ*. - In physics, the torsional constant of an oscillator is given by
*κ*. - In physics, the coupling coefficient in magnetostatics is represented by
*κ*. - In fluid dynamics, the von Kármán constant is represented by
*κ*. - In thermodynamics, the compressibility of a compound is given by
*κ*.

- Engineering

- In structural engineering,
*κ*is the ratio of the smaller factored moment to the larger factored moment and is used to calculate the critical elastic moment of an unbraced steel member. - In electrical engineering,
*κ*is the multiplication factor, a function of the*R*/*X*ratio of the equivalent power system network, which is used in calculating the peak short-circuit current of a system fault.*κ*is also used to denote conductivity, the reciprocal of resistivity, rho.

- Biology and biomedical science

- In biology, kappa and kappa prime are important nucleotide motifs for a tertiary interaction of group II introns.
- In biology, kappa designates a subtype of an antibody component.
- In pharmacology, kappa represents a type of opioid receptor.

- Psychology and psychiatry

- In psychology and psychiatry, kappa represents a measure of diagnostic reliability.

- Economics

- In macroeconomics, kappa represents the capital-utilization rate.
^{[citation needed]}

### Uppercase (Κ)

- History

- In textual criticism, the Byzantine text-type (from Κοινη,
*Koine*, the common text).

- Mathematics and statistics

- In set theory, kappa is often used to denote an ordinal that is also a cardinal.

- Chemistry

- In chemistry, kappa is used to denote the denticity of the compound.
- In pulping, the kappa number represents the amount of an oxidizing agent required for bleaching a pulp.

## Character encodings

Preview | Κ | κ | ϰ | Ⲕ | ⲕ | |||||
---|---|---|---|---|---|---|---|---|---|---|

Unicode name | GREEK CAPITAL LETTER KAPPA | GREEK SMALL LETTER KAPPA | GREEK KAPPA SYMBOL | COPTIC CAPITAL LETTER KAPA | COPTIC SMALL LETTER KAPA | |||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 922 | U+039A | 954 | U+03BA | 1008 | U+03F0 | 11412 | U+2C94 | 11413 | U+2C95 |

UTF-8 | 206 154 | CE 9A | 206 186 | CE BA | 207 176 | CF B0 | 226 178 148 | E2 B2 94 | 226 178 149 | E2 B2 95 |

Numeric character reference | Κ | Κ | κ | κ | ϰ | ϰ | Ⲕ | Ⲕ | ⲕ | ⲕ |

Named character reference | Κ | κ | &kappav, &varkappa | |||||||

DOS Greek | 137 | 89 | 161 | A1 | ||||||

DOS Greek-2 | 181 | B5 | 228 | E4 | ||||||

Windows 1253 | 202 | CA | 234 | EA | ||||||

TeX | \kappa |

- Mathematical Kappa

Preview | 𝚱 | 𝛋 | 𝛞 | 𝛫 | 𝜅 | |||||
---|---|---|---|---|---|---|---|---|---|---|

Unicode name | MATHEMATICAL BOLD CAPITAL KAPPA | MATHEMATICAL BOLD SMALL KAPPA | MATHEMATICAL BOLD KAPPA SYMBOL | MATHEMATICAL ITALIC CAPITAL KAPPA | MATHEMATICAL ITALIC SMALL KAPPA | |||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120497 | U+1D6B1 | 120523 | U+1D6CB | 120542 | U+1D6DE | 120555 | U+1D6EB | 120581 | U+1D705 |

UTF-8 | 240 157 154 177 | F0 9D 9A B1 | 240 157 155 139 | F0 9D 9B 8B | 240 157 155 158 | F0 9D 9B 9E | 240 157 155 171 | F0 9D 9B AB | 240 157 156 133 | F0 9D 9C 85 |

UTF-16 | 55349 57009 | D835 DEB1 | 55349 57035 | D835 DECB | 55349 57054 | D835 DEDE | 55349 57067 | D835 DEEB | 55349 57093 | D835 DF05 |

Numeric character reference | 𝚱 | 𝚱 | 𝛋 | 𝛋 | 𝛞 | 𝛞 | 𝛫 | 𝛫 | 𝜅 | 𝜅 |

Preview | 𝜘 | 𝜥 | 𝜿 | 𝝒 | 𝝟 | |||||
---|---|---|---|---|---|---|---|---|---|---|

Unicode name | MATHEMATICAL ITALIC KAPPA SYMBOL | MATHEMATICAL BOLD ITALIC CAPITAL KAPPA | MATHEMATICAL BOLD ITALIC SMALL KAPPA | MATHEMATICAL BOLD ITALIC KAPPA SYMBOL | MATHEMATICAL SANS-SERIF BOLD CAPITAL KAPPA | |||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120600 | U+1D718 | 120613 | U+1D725 | 120639 | U+1D73F | 120658 | U+1D752 | 120671 | U+1D75F |

UTF-8 | 240 157 156 152 | F0 9D 9C 98 | 240 157 156 165 | F0 9D 9C A5 | 240 157 156 191 | F0 9D 9C BF | 240 157 157 146 | F0 9D 9D 92 | 240 157 157 159 | F0 9D 9D 9F |

UTF-16 | 55349 57112 | D835 DF18 | 55349 57125 | D835 DF25 | 55349 57151 | D835 DF3F | 55349 57170 | D835 DF52 | 55349 57183 | D835 DF5F |

Numeric character reference | 𝜘 | 𝜘 | 𝜥 | 𝜥 | 𝜿 | 𝜿 | 𝝒 | 𝝒 | 𝝟 | 𝝟 |

Preview | 𝝹 | 𝞌 | 𝞙 | 𝞳 | 𝟆 | |||||
---|---|---|---|---|---|---|---|---|---|---|

Unicode name | MATHEMATICAL SANS-SERIF BOLD SMALL KAPPA | MATHEMATICAL SANS-SERIF BOLD KAPPA SYMBOL | MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL KAPPA | MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL KAPPA | MATHEMATICAL SANS-SERIF BOLD ITALIC KAPPA SYMBOL | |||||

Encodings | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | hex |

Unicode | 120697 | U+1D779 | 120716 | U+1D78C | 120729 | U+1D799 | 120755 | U+1D7B3 | 120774 | U+1D7C6 |

UTF-8 | 240 157 157 185 | F0 9D 9D B9 | 240 157 158 140 | F0 9D 9E 8C | 240 157 158 153 | F0 9D 9E 99 | 240 157 158 179 | F0 9D 9E B3 | 240 157 159 134 | F0 9D 9F 86 |

UTF-16 | 55349 57209 | D835 DF79 | 55349 57228 | D835 DF8C | 55349 57241 | D835 DF99 | 55349 57267 | D835 DFB3 | 55349 57286 | D835 DFC6 |

Numeric character reference | 𝝹 | 𝝹 | 𝞌 | 𝞌 | 𝞙 | 𝞙 | 𝞳 | 𝞳 | 𝟆 | 𝟆 |

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.

## References

**^**"kappa".*Oxford English Dictionary*(Online ed.). Oxford University Press. (Subscription or participating institution membership required.)