RKM code

The RKM code,[1] also referred to as "letter and numeral code for resistance and capacitance values and tolerances",[1] "letter and digit code for resistance and capacitance values and tolerances",[2][3] or "R notation"[citation needed], is a notation to specify resistor and capacitor values defined in the international standard IEC 60062 (formerly IEC 62) since 1952. It is also adopted by various other standards including DIN 40825 (1973), BS 1852 (1974), IS 8186 (1976) and EN 60062 (1993). The significantly updated IEC 60062:2016 comprises the most recent release of the standard.[1]


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.

Part value codeEdit

Examples of resistance values[4]
R47 0.47 ohm
4R7 4.7 ohm
470R 470 ohm
4K7 4.7 kilohm
47K 47 kilohm
47K3 47.3 kilohm
470K 470 kilohm
4M7 4.7 megohm

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.

Code letter Prefix Multiplier[5]
Resistance [Ω] Capacitance [F] Name Symbol (SI) Base 10 Base 1000 Value
- p (P[nb 2]) pico- p ×10−12 ×1000−4 ×0.000000000001
- n (N[nb 2]) nano- n ×10−9 ×1000−3 ×0.000000001
- µ (u, U[nb 2]) micro- µ ×10−6 ×1000−2 ×0.000001
L m (M[nb 1][nb 2]) milli- m ×10−3 ×1000−1 ×0.001
R (E[nb 3]) F - - ×100 ×10000 ×1
K (k[nb 4]) - kilo- k ×103 ×10001 ×1000
M[nb 1] - mega- M ×106 ×10002 ×1000000
G - giga- G ×109 ×10003 ×1000000000
T - tera- T ×1012 ×10004 ×1000000000000

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,[6] 1983[7]), DIN 66030 (Vornorm 1973;[8] 1980,[9][10] 2002[11]) 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.

Tolerance codeEdit

Letter code for resistance and capacitance tolerances:

Code letter Tolerance
Resistance Capacitance Relative Absolute
Symmetrical Asymmetrical C <10 pF only
A A variable (±0.05%) variable variable
B B ±0.1% N/A
C C ±0.25% N/A ±0.25 pF
D D ±0.5% N/A ±0.5 pF
E ±0.005% N/A N/A
F F ±1.0% N/A ±1.0 pF
G G ±2.0% N/A ±2.0 pF
H H ±3.0% N/A N/A
J J ±5.0% N/A N/A
K K ±10% N/A N/A
L ±0.01% N/A N/A
M M ±20% N/A N/A
N ±30% N/A N/A
P ±0.02% N/A N/A
Q N/A −10/+30% N/A
S N/A −20/+50% N/A
T N/A −10/+50% N/A
W ±0.05% N/A N/A
Z N/A −20/+80% N/A

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.[12]

Temperature coefficient codeEdit

Letter codes for resistor temperature coefficients:

Code letter ppm/K
K 1
M 5
P 15
Q 25
R 50
S 100
U 250
Z other

Production date codeEdit

  • 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)

Similar codesEdit

A similar not standardized notation using the unit symbol instead of a decimal separator is sometimes used to indicate voltages (3V3 for 3.3 V, or 1V8 for 1.8 V) in contexts where a decimal separator would be inappropriate (e.g. in signal names or file names).

Corresponding standardsEdit

  • 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)[16]
  • 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[17] (related to IEC 60062:1974)
  • BS EN 60062:1994[18]
  • BS EN 60062:2005[19]
  • BS EN 60062:2016[20]
  • 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[15] (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[21]
  • IS 8186-1976[22] (related to IEC 62:1974)
  • JIS C 5062
  • TGL 31667[23]

See alsoEdit


  1. ^ a b c The letter M was an exception to the rule that all different letters are supposed to be used for resistances and capacitances. Today, a lowercase letter m should be used for capacitances whenever possible to avoid confusion.
  2. ^ a b c d e In old issues of the IEC 60062 standard, uppercase Latin letters were not only used for resistances, but also for capacitance values, whereas newer issues specifically use lowercase letters for capacitors (except for the special case of F).
  3. ^ The usage of the Latin letter E instead of R is not standardized in IEC 60062, but nevertheless sometimes seen in practice. It stems from the fact, that R is used in symbolic names for resistors as well, and it is also used in a similar fashion but with incompatible meaning in other part marking codes. It may therefore cause confusion in some contexts. Visually, the letter E loosely resembles a small Greek letter omega (ω) turned sideways. Historically (f.e. in pre-WWII documents), before ohms were denoted using the uppercase Greek omega (Ω), a small omega (ω) was sometimes used for this purpose as well, as in 56ω for 56 Ω. However, the letter E is conflictive with the similar looking but incompatible E notation in engineering, and it may therefore cause considerable confusion as well.
  4. ^ The IEC 60062 standard prescribes the usage of an uppercase Latin letter K only, however, a lowercase k is often seen in schematics and bills of materials probably because the corresponding SI prefix is defined as a lowercase k.
  5. ^ In order to reduce the risk for read errors, the letters G (6), I (J, 1), O (0, Q, D), Q (O, D, 0), Y, Z (2) are not used as their glyphs look similar to other letters and digits.
  6. ^ Due to the ambiguity of many month initials (A, J, M) the code for the most part uses digits. Since letter O is easily confused with digit 0, the code is arranged so that the letter O is used for October, the tenth month, rather than for January.


  1. ^ a b c d "IEC 60062:2016-07" (6 ed.). July 2016. Archived from the original on 2018-07-23. Retrieved 2018-07-23. [1]
  2. ^ a b https://webstore.iec.ch/p-preview/info_iec60062%7Bed5.0%7Den.pdf
  3. ^ "14. Letter and digit code for R & C values". Units & Symbols for Electrical & Electronic Engineers (PDF). The Institution of Engineering and Technology (IET). 2016 [1985]. p. 29. Archived (PDF) from the original on 2020-08-07. Retrieved 2021-04-25. (37 pages)
  4. ^ "Resistors - Letters and Digit Codes. Letter and digit codes to indicating resistor values". The Engineering ToolBox. 2010. Archived from the original on 2020-06-21. Retrieved 2020-05-14.
  5. ^ Tooley, Mike (2011-07-19). "BS1852 Resistor Coding". Matrix - Electronic circuits and components. Archived from the original on 2016-12-20. Retrieved 2020-05-14.
  6. ^ ISO 2955-1974: lnformation processing - Representations of SI and other units for use in systems with limited character sets (1 ed.). 1974.
  7. ^ "Table 2". ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets (PDF) (2 ed.). 1983-05-15. Retrieved 2016-12-14. [2]
  8. ^ Vornorm DIN 66030 [Preliminary standard DIN 66030] (in German). January 1973.
  9. ^ DIN 66030: Informationsverarbeitung - Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat [Information processing; representations for names of units to be used in systems with limited graphic character sets] (in German) (1 ed.). Beuth Verlag [de]. November 1980. Retrieved 2016-12-14.
  10. ^ "Neue Normen für die Informationsverarbeitung". Computerwoche (in German). 1981-01-09. Archived from the original on 2016-12-14. Retrieved 2016-12-14.
  11. ^ DIN 66030:2002-05 - Informationstechnik - Darstellung von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat [Information technology - Representation of SI and other units in systems with limited character sets] (in German). Beuth Verlag [de]. May 2002. Retrieved 2016-12-14.
  12. ^ Buttner, Harold H.; Kohlhaas, H. T.; Mann, F. J., eds. (1946). "Chapter 3: Audio and radio design". Reference Data for Radio Engineers (PDF) (2 ed.). {[Federal Telephone and Radio Corporation]] (FTR). pp. 52, 55. Archived (PDF) from the original on 2018-05-16. Retrieved 2020-01-03. (NB. While the tolerance codes according to AWS/JAN are listed in this second edition of the book, they are not listed in the 1943 original edition.)
  13. ^ a b c d e f g h i j k l m n o p q "Precision and Power Resistors (ISA)" (PDF). Swansea, MA, USA: Isotek Corporation / Isabellenhütte [de]. Archived (PDF) from the original on 2017-02-07. Retrieved 2017-02-07.
  14. ^ a b c d e f g h i j k l "Production date code marking system according to IEC 60062, clause 5.1 Two-character code (year/month)" (PDF). Iskra Kondenzatorji. 2017. Archived (PDF) from the original on 2017-02-07. Retrieved 2017-02-07. (NB. Date codes for 2016 and 2017 are obviously wrong.)
  15. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ГОСТ IEC 60062-2014 (PDF) (in Russian). GOST (ГОСТ). 2014.
  16. ^ IEC 60062:1974
  17. ^ BS 1852:1975.
  18. ^ BS EN 60062:1994.
  19. ^ BS EN 60062:2005.
  20. ^ BS EN 60062:2016.
  21. ^ "www.worldstdindex.com". www.worldstdindex.com.
  22. ^ IS : 8186-1976 (PDF). 1977 [1976]. Archived (PDF) from the original on 2016-12-14. Retrieved 2016-12-14.
  23. ^ TGL 31667: Bauelemente der Elektronik; Kennzeichnung; Herstellungsdatum [TGL 31667: Electronic Components; Designation; Date of Manufacture] (PDF) (in German). Leipzig, Germany: Verlag für Standardisierung. October 1979. Archived (PDF) from the original on 2021-01-28. Retrieved 2018-01-09.