R (disambiguation)

R is the eighteenth letter of the Latin alphabet.

R may also refer to:

Mathematics

R-value (insulation), a non-SI measure of thermal resistance used in housing insulation
R-value (soils), property of soils used in pavement design
An electronic resistor, e.g. in circuit diagrams
The R-# refrigerant numbering system
In fracture mechanics, the ratio between the minimum and maximum stresses

The spectral resolution in astronomy
The symbol given to the molar gas constant in chemistry
A stellar classification for orangish or K carbon stars
R (cross section ratio), the ratio of hadronic to muonic cross sections
Roentgen (unit), a unit of measurement for ionizing radiation such as X-ray and gamma rays
The Rydberg constant, a physical constant relating to energy levels of electrons within atoms
R, a label that denotes one of two chiral center configurations in the R/S system
A side chain (an unspecified group of atoms) in a chemical or structural formula
Arginine, an amino acid
Relatedness, in biology
r, representing population growth rate in the r/K selection theory of ecology
Haplogroup R (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
Haplogroup R (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
ATC code R Respiratory system, a section of the Anatomical Therapeutic Chemical Classification System
In the thermodynamic temperature scale °R may refer to the Rankine scale or to the Réaumur scale or even to the Rømer scale

R, denoting a member of the Republican Party in American politics
R, denoting The Crown, Rex (King) or Regina (Queen) in Commonwealth nations
R (cable operator), a telecommunications company
A film rating in the Motion Picture Association of America film rating system and in the Canadian Home Video Rating System.
Rolled R, the alveolar trill of Spanish, Italian, & Arabic languages
The three Rs of Reading, wRiting and aRithmetic
In The World Is Not Enough, a character played by John Cleese
R·Type, an arcade video game
R: Rock'n Riders, a PlayStation video game
®, the registered trademark symbol
The South African rand currency
Ryder's NYSE ticker symbol
R (New York City Subway service)
R, the military designation for a reconnaissance aircraft.
Volkswagen Golf R
R (film), 2010 film by Danish screenwriter and film director, Tobias Lindholm