Latin Capital Letter K
In the sciences, uppercase 'K' carries exceptional weight — it is the SI symbol for the kelvin (thermodynamic temperature) and the chemical symbol for potassium (from Latin kalium), making it one of the most overloaded single letters in technical writing. The eleventh letter of the Latin alphabet, it sits at ASCII code point 75 (0x4B), 32 below its lowercase counterpart 'k' at 107 (0x6B), maintaining the single-bit case offset shared by all ASCII A–Z / a–z pairs. In English, 'K' appears routinely in abbreviations, unit symbols, and proper nouns.
Technical Details
Code Example
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#define KB (1024) // 1 KiB#define MB (KB * 1024) // 1 MiBsize_t buffer_size = 64 * KB; // 64 KiB
Common Usage
Scientific symbols and SI usage: Uppercase 'K' denotes the kelvin, the SI base unit of thermodynamic temperature — notably written without a degree symbol (100 K, not 100° K) since 1967. It is also the chemical symbol for potassium (atomic number 19, from Latin kalium). In physics, K frequently represents kinetic energy, the bulk modulus, and equilibrium constants — context alone disambiguates, making 'K' one of the most polysemous letters in scientific notation.
Computing and the kilo confusion: Historically, uppercase 'K' was used loosely to mean 1024 (2¹⁰) in computing contexts — as in '64K RAM' — blurring the SI prefix kilo (1000). The IEC standard introduced 'Ki' (kibibyte, KiB) to resolve this ambiguity, but informal use of 'K' for 1024 persists in embedded systems, retro computing, and everyday developer shorthand. The distinction between KB (kilobyte, often ambiguous) and kB (1000 bytes) continues to cause confusion.
Silent K and English phonetics: Uppercase 'K' leads a well-known set of English words where it is entirely silent before 'n' — Knee, Knife, Knight, Knot, Know. This silent-K pattern is a fossil of Old English and Germanic pronunciation, where the /k/ was originally voiced. In modern English, the 'kn-' cluster reduces to /n/, though related German and Dutch cognates often preserve the /k/ sound.
Diacritical variants: Uppercase 'K' has a small but linguistically important set of modified forms. Ķ (cedilla) is a distinct letter in Latvian representing a palatalized velar stop, Ǩ (caron) appears in Skolt Sami, and Ḳ (dot below) is used in various transliteration systems for Arabic and other Semitic languages. Ƙ (hook) appears in several African language orthographies, particularly Hausa, where it represents an ejective or implosive consonant.
Scientific symbols and SI usage: Uppercase 'K' denotes the kelvin, the SI base unit of thermodynamic temperature — notably written without a degree symbol (100 K, not 100° K) since 1967. It is also the chemical symbol for potassium (atomic number 19, from Latin kalium). In physics, K frequently represents kinetic energy, the bulk modulus, and equilibrium constants — context alone disambiguates, making 'K' one of the most polysemous letters in scientific notation.
Computing and the kilo confusion: Historically, uppercase 'K' was used loosely to mean 1024 (2¹⁰) in computing contexts — as in '64K RAM' — blurring the SI prefix kilo (1000). The IEC standard introduced 'Ki' (kibibyte, KiB) to resolve this ambiguity, but informal use of 'K' for 1024 persists in embedded systems, retro computing, and everyday developer shorthand. The distinction between KB (kilobyte, often ambiguous) and kB (1000 bytes) continues to cause confusion.
Silent K and English phonetics: Uppercase 'K' leads a well-known set of English words where it is entirely silent before 'n' — Knee, Knife, Knight, Knot, Know. This silent-K pattern is a fossil of Old English and Germanic pronunciation, where the /k/ was originally voiced. In modern English, the 'kn-' cluster reduces to /n/, though related German and Dutch cognates often preserve the /k/ sound.
Diacritical variants: Uppercase 'K' has a small but linguistically important set of modified forms. Ķ (cedilla) is a distinct letter in Latvian representing a palatalized velar stop, Ǩ (caron) appears in Skolt Sami, and Ḳ (dot below) is used in various transliteration systems for Arabic and other Semitic languages. Ƙ (hook) appears in several African language orthographies, particularly Hausa, where it represents an ejective or implosive consonant.