Latin Capital Letter U
Inseparable from Unicode itself, uppercase 'U' is the letter that prefixes every code point notation in the standard (U+0041, U+1F600) — making it perhaps the single most-seen character in encoding documentation. It sits at ASCII code point 85 (0x55), exactly 32 below its lowercase counterpart 'u' at 117 (0x75), maintaining the single-bit case offset (bit 5) shared by all ASCII A–Z / a–z pairs. In English, 'U' appears at moderate frequency as an uppercase letter, most often at sentence openings and in acronyms like URL, USB, and UI.
Technical Details
Code Example
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// Unsigned suffixunsigned int u = 100U;unsigned long ul = 1000UL;unsigned long long ull = 1000000ULL;
Common Usage
Unicode notation and escape sequences: The prefix U+ is the standard notation for Unicode code points (e.g., U+0055 for 'U' itself), appearing throughout encoding specifications, character databases, and internationalization documentation. In programming, the lowercase \u escape denotes a Unicode code point in JavaScript, Java, Python, and C# string literals (e.g., \u0055), while Python additionally supports the uppercase \U prefix for full 32-bit code points (\U0001F600) — a case distinction that catches many developers off guard.
Biology and IT standards: In molecular biology, 'U' represents uracil, the nucleotide base that replaces thymine in RNA — making it essential in transcription diagrams, RNA sequence data, and bioinformatics tools that distinguish DNA from RNA strands. In data center and audio/video infrastructure, 'U' denotes a rack unit (1U = 1.75 inches / 44.45 mm), the standard vertical measurement for server chassis, network switches, and rack-mounted equipment — a 2U server is twice the height of a 1U unit, and the notation appears on virtually every hardware spec sheet.
Mathematics — sets and union: Uppercase 'U' is the standard symbol for internal energy in thermodynamics (ΔU = Q − W) and for uranium (atomic number 92) in chemistry. In mathematics, the set union operator ∪ (U+222A) borrows its visual form from the letter 'U', and students frequently search for the 'U symbol' when seeking the union of sets — though the operator is a distinct Unicode character from the Latin letter. This visual kinship makes 'U' one of the most cross-referenced letters between typography and mathematical notation.
Diacritical variants: Uppercase 'U' supports a rich set of accented forms — Ù, Ú, Û, Ü, Ů, Ū, Ų, Ũ — spanning numerous orthographies. Ü (diaeresis) is a distinct letter in Turkish and Azerbaijani and carries phonemic weight in German and Hungarian, Ů (ring above) is unique to Czech, and Ū (macron) marks long vowels in Māori, Latvian, and romanized Japanese (rōmaji). In Lithuanian, Ų (ogonek) represents a historically nasalized vowel that has since lost its nasal quality.
Unicode notation and escape sequences: The prefix U+ is the standard notation for Unicode code points (e.g., U+0055 for 'U' itself), appearing throughout encoding specifications, character databases, and internationalization documentation. In programming, the lowercase \u escape denotes a Unicode code point in JavaScript, Java, Python, and C# string literals (e.g., \u0055), while Python additionally supports the uppercase \U prefix for full 32-bit code points (\U0001F600) — a case distinction that catches many developers off guard.
Biology and IT standards: In molecular biology, 'U' represents uracil, the nucleotide base that replaces thymine in RNA — making it essential in transcription diagrams, RNA sequence data, and bioinformatics tools that distinguish DNA from RNA strands. In data center and audio/video infrastructure, 'U' denotes a rack unit (1U = 1.75 inches / 44.45 mm), the standard vertical measurement for server chassis, network switches, and rack-mounted equipment — a 2U server is twice the height of a 1U unit, and the notation appears on virtually every hardware spec sheet.
Mathematics — sets and union: Uppercase 'U' is the standard symbol for internal energy in thermodynamics (ΔU = Q − W) and for uranium (atomic number 92) in chemistry. In mathematics, the set union operator ∪ (U+222A) borrows its visual form from the letter 'U', and students frequently search for the 'U symbol' when seeking the union of sets — though the operator is a distinct Unicode character from the Latin letter. This visual kinship makes 'U' one of the most cross-referenced letters between typography and mathematical notation.
Diacritical variants: Uppercase 'U' supports a rich set of accented forms — Ù, Ú, Û, Ü, Ů, Ū, Ų, Ũ — spanning numerous orthographies. Ü (diaeresis) is a distinct letter in Turkish and Azerbaijani and carries phonemic weight in German and Hungarian, Ů (ring above) is unique to Czech, and Ū (macron) marks long vowels in Māori, Latvian, and romanized Japanese (rōmaji). In Lithuanian, Ų (ogonek) represents a historically nasalized vowel that has since lost its nasal quality.