RKM code

Originally meant also as part marking code, this shorthand notation is widely used in electrical engineering to denote the values of resistors and capacitors in circuit diagrams and in the production of electronic circuits (for example in bills of material and in silk screens). This method avoids overlooking the decimal separator, which may not be rendered reliably on components or when duplicating documents.

The standards also define a color code for fixed resistors.

For brevity, the notation omits to always specify the unit (ohm or farad) explicitly and instead relies on implicit knowledge raised from the usage of specific letters either only for resistors or for capacitors,[nb 1] the case used (uppercase letters are typically used for resistors, lowercase letters for capacitors),[nb 2] a part's appearance, and the context.

The notation also avoids using a decimal separator and replaces it by a letter associated with the prefix symbol for the particular value.

This is not only for brevity (for example when printed on the part or PCB), but also to circumvent the problem that decimal separators tend to "disappear" when photocopying printed circuit diagrams.

The code letters are loosely related to the corresponding SI prefix, but there are several exceptions, where the capitalization differs or alternative letters are used.

For example, 8K2 indicates a resistor value of 8.2 kΩ. Additional zeros imply tighter tolerance, for example 15M0.

When the value can be expressed without the need for a prefix, an "R" is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω.

For resistances, the standard dictates the use of the uppercase letters L (for 10⁻³), R (for 10⁰ = 1), K (for 10³), M (for 10⁶), and G (for 10⁹) to be used instead of the decimal point.

The usage of the letter R instead of the SI unit symbol Ω for ohms stems from the fact that the Greek letter Ω is absent from most older character encodings (though it is present in the now-ubiquitous Unicode) and therefore is sometimes impossible to reproduce, in particular in some CAD/CAM environments. The letter R was chosen because visually it loosely resembles the Ω glyph, and also because it works nicely as a mnemonic for resistance in many languages.

The letters G and T weren't part of the first issue of the standard, which pre-dates the introduction of the SI system (hence the name "RKM code"), but were added after the adoption of the corresponding SI prefixes.

The introduction of the letter L in more recent issues of the standard (instead of an SI prefix m for milli) is justified to maintain the rule of only using uppercase letters for resistances (the otherwise resulting M was already in use for mega).

Similar, the standard prescribes the following lowercase letters for capacitances to be used instead of the decimal point: p (for 10⁻¹²), n (for 10⁻⁹), µ (for 10⁻⁶), m (for 10⁻³), but uppercase F (for 10⁰ = 1) for farad.

The letters p and n weren't part of the first issue of the standard, but were added after the adoption of the corresponding SI prefixes.

In cases where the Greek letter µ is not available, the standard allows it to be replaced by u (or U, when only uppercase letters are available). This usage of u instead of µ is also in line with ISO 2955 (1974,[5] 1983[6]), DIN 66030 (Vornorm 1973;[7] 1980,[8][9] 2002[10]) and BS 6430 (1983), which allow the prefix μ to be substituted by the letter u (or U) in circumstances in which only the Latin alphabet is available.

Letter code for resistance and capacitance tolerances:

Before the introduction of the RKM code, some of the letters for symmetrical tolerances (viz. G, J, K, M) were already used in US military contexts following the American War Standard (AWS) and Joint Army-Navy Specifications (JAN) since the mid-1940s.[11]

Letter codes for resistor temperature coefficients:

• First character: Year of production[nb 5]
  • A = 2010,[12][13] 1990,[14] 1970[14]
  • B = 2011,[12][13] 1991,[14] 1971[14]
  • C = 2012,[12][13] 1992,[14] 1972[14]
  • D = 2013,[12][13] 1993,[14] 1973[14]
  • E = 2014,[12][13] 1994,[14] 1974[14]
  • F = 2015,[12][13] 1995,[14] 1975[14]
  • H = 2016,[12] 1996,[14] 1976[14]
  • J = 2017,[12] 1997,[14] 1977[14]
  • K = 2018,[12] 1998,[14] 1978[14]
  • L = 2019,[12] 1999,[14] 1979[14]
  • M = 2020,[12] 2000,[14] 1980[14]
  • N = 2021,[12] 2001,[14] 1981[14]
  • P = 2022,[12] 2002,[14] 1982[14]
  • R = 2023,[12] 2003,[14] 1983[14]
  • S = 2024,[12] 2004,[13][14] 1984[14]
  • T = 2025,[12] 2005,[13][14] 1985[14]
  • U = 2006,[13] 1986[14]
  • V = 2007,[13][14] 1987[14]
  • W = 2008,[13][14] 1988[14]
  • X = 2009,[12][13][14] 1989[14]

• Second character: Month of production[nb 6]
  • 1 to 9 = January to September
  • O = October
  • N = November
  • D = December

Example: V8 = August 2007 (or August 1987)

• IEC 62:1952 (aka IEC 60062:1952), first edition, 1952-01-01
• IEC 62:1968 (aka IEC 60062:1968), second edition, 1968-01-01
• IEC 62:1968/AMD1:1968 (aka IEC 60062:1968/AMD1:1968), amended second edition, 1968-12-31
• IEC 62:1974 (aka IEC 60062:1974)[15]
• IEC 62:1974/AMD1:1988 (aka IEC 60062:1974/AMD1:1988), amended third edition, 1988-04-30
• IEC 62:1974/AMD2:1989 (aka IEC 60062:1974/AMD2:1989), amended third edition, 1989-01-01
• IEC 62:1992 (aka IEC 60062:1992), fourth edition, 1992-03-15
• IEC 62:1992/AMD1:1995 (aka IEC 60062:1992/AMD1:1995), amended fourth edition, 1995-06-19
• IEC 60062:2004 (fifth edition, 2004-11-08)[2]
• IEC 60062:2016 (sixth edition, 2016-07-12)[1]
• IEC 60062:2016/COR1:2016 (corrected sixth edition, 2016-12-05)
• EN 60062:1993
• EN 60062:1994 (1994-10)
• EN 60062:2005
• EN 60062:2016
• BS 1852:1975[16] (related to IEC 60062:1974)
• BS EN 60062:1994[17]
• BS EN 60062:2005[18]
• BS EN 60062:2016[19]
• DIN 40825:1973-04 (capacitor/resistor value code), DIN 41314:1975-12 (date code)
• DIN IEC 62:1985-12 (aka DIN IEC 60062:1985-12)
• DIN IEC 62:1989-10 (aka DIN IEC 60062:1989-10)
• DIN IEC 62:1990-11 (aka DIN IEC 60062:1990-11)
• DIN IEC 62:1993-03 (aka DIN IEC 60062:1993-03)
• DIN EN 60062:1997-09
• DIN EN 60062:2001-11
• DIN EN 60062:2005-11
• ČSN EN 60062
• DS/EN 60062
• EVS-EN 60062
• (GOST) ГОСТ IEC 60062-2014[14] (related to IEC 60062-2004)
• ILNAS-EN 60062
• I.S. EN 60062
• NEN EN IEC 60062
• NF EN 60062
• ÖVE/ÖNORM EN 60062
• PN-EN 60062
• prМКС EN 60062
• SN EN 60062
• TS 2932 EN 60062
• UNE-EN 60062

• BIS IS 4114-1967[20]
• IS 8186-1976[21] (related to IEC 62:1974)
• JIS C 5062
• TGL 31667[22]

• Electronic color code
• SI prefix
• Metric prefix
• Engineering notation
• E notation
• Cifrão (a similar scheme for a currency)