Electronic color code

A 2.26 kΩ, 1%-precision resistor with 5 color bands (E96 series), from top, 2-2-6-1-1; the last two brown bands indicate the multiplier (×10) and the tolerance (1%).

An electronic color code is a system which wordlessly identifies either the functions of cables and connections, or the types and variants of electronic components. Codes for cables and connections range from the use of pink, blue, and green connectors on computer sound cards, to early attempts at standardizing the colors of battery, loudspeaker, and antenna wires of radio sets in the 1920s, to the 25-pair color code, used in telecommunications cables. Among the component identification applications, those used on resistors are most widespread, with usage on inductors also popular, while in the past, many variations were applied to capacitors, diodes, and other part types.

History

RMA resistor color code guide, ca. 1945–1950

Before standardization, some manufacturers used their own color codings on the fixed resistors in their radio sets, seemingly choosing a random color for each part stock number. Then, in 1930, a new code started coming into wide usage among radio makers. This new style encoded the resistance value of each part by means of one background paint color and usually, two additional paint marks. The Radio Manufacturers Association (RMA) gave its endorsement of this coding around 1931. This all-over painted, "body-end-dot" coding style, while most vividly associated with pre-war radio equipment, did live on for a while, and was still in use in the 1960s.

In 1935, advertisements appeared for resistors coded with a sequence of color bands including one acting as a tolerance indicator; the RMA adopted a standard for this alternative style by 1941. A 1943 reference book, Mechanical Practice gives an early description of a further development. While the 1935 banded style only called for two digit bands before the band that specifies a "multiplying value", coded as an exponent, the new variation had three, bringing the total number of bands including the tolerance to five, as opposed to just three or four. This might seem to indicate that even at that early date, the use of a four–five rule became necessary in decoding banded resistors; in going from four to five in the total count of bands, that is where the number of digit-encoding bands increases from two to three, moving the exponent band from the third to the fourth position. In practice this was not a very important rule to memorize back then, as actual resistors showing the three-digit coding innovation remained scarce for twenty years afterwards. Eight decades later, application of the rule in some form is routinely required, but now a big part of the art of reading random-sourced resistors is, recognizing the exceptions, those tricky cases where resistance codings do not follow the rule.

Over many decades, as the organization name changed (RMA, RTMA, RETMA, EIA) so was the name of the code. Though known most recently as EIA color code, the four name variations are found in books, magazines, catalogs, and other documents over more than 95 years.

In 1952, the International Electrotechnical Commission (IEC) published a fork of the RMA's banded resistor concept as IEC 62:1952; although it did not expand to include three-digit codings following a four–five rule until the 1974 edition, its successors and national versions/translations are widely referenced today. Starting with the 1968 edition it added in the widely used "RKM codes" for printed text component values on resistors and capacitors. Successive revisions, up to the current IEC 60062:2016, added more optional features to the resistor color code, but also diverged from the EIA versions.

One standardized color code scheme for capacitors was in use by 1934, although some radio makers kept using random-picked color codes on these longer than they did on resistors. (At that point, most were still calling these "condensers", an older term.) There were many variations of flat postage stamp/domino-style mica and paper dielectric capacitors with paint dots; tubular capacitors with a sequence of spots or bands also date to the 1940s. Eventually many more styles were produced using mica, paper, ceramic, glass, and plastics for the dielectric, also many tantalum types, not all codings directly published by the RMA and successors, some with dots, some with bands, some with layer-dipped paint. A 1949 article detailed nine marking types in use by that time, but the proliferation of styles was just getting started then. Some later ceramic-dielectric ones from the VCR era of roughly 1980 onward look a lot like modern small axial-leaded resistors. Today, while color-coded "caps" are less commonly encountered, the layer-dipped "tropical fish" ones are still preferred by some, and recent reproductions of certain old tubular capacitor types have been embellished with replica "bumble-bee" color bands, suitable to make any classic-style electric guitar more authentic.

Schemes for color-coding small inductors, (A.K.A. radio frequency chokes, coils, etc.) were in use by 1950; as with the capacitors, some types do look a lot like modern small resistors. For reading, while many recent ones decode like common resistors, giving an inductance value in microhenries, older ones and some current ones are more complicated; unlike resistors, a gold or silver band may be at either end, or both, and there may be no exponent band.

Small semiconductor diodes/rectifiers were being marked with color bands by 1958. Some Zener/avalanche-breakdown diodes have paint bands that indicate their main characteristic of interest, which is, their nominal rated Zener voltage. More commonly, a type number is indicated using one of several variants that support the U.S. JEDEC "1N" series (Glass diodes marked this way were common in the 1960s.) and European Pro Electron numbering schemes. Proprietary arbitrary codings were used by some; Hitachi made diodes with bands of designer colors such as "verdure" and "yellow ocher". Many later-production glass diodes have only one or two color bands, indicating a broad type category.

Several complex color coding systems for plastic-cased transistors were in use in the Soviet sphere. The U.S. standard for diodes allows application to transistors but seems to have been little used for this. Usually when color markings are found on U.S.-style small plastic transistors that have printed numbering also, they indicate a bin-sort code or something proprietary.

By 1970, disc-shaped thermistors and voltage dependent resistors/varistors were being made with color coding in the form of layer-dipped paint; these may be confused with some ceramic disk capacitors which are painted similarly. There are also tubular, axial-leaded styles of varistors which have their own look which differentiates them from other components.

There is even a color band coding standard for fuses, published in 1988 as IEC 127, and adopted in national variants covering both cartridge types that look like fuses and also, miniature types that look like modern small resistors.

The paint pigment used for the number seven, according to some British sources, is supposed to be a "dark violet"; others in the British Commonwealth have called it mauve. The general consensus of references world-wide through the decades would be a simple violet, although, in the early years there are several sources that call it purple, and even a vote for lavender may be found.

A good skill to learn along with reading the codes themselves is doing the up-front step of identifying the basic type of a component, whether it is a resistor, capacitor, inductor, fuse, diode, or other. The color band system has the advantage of being readable, by people with good color vision, from multiple directions, if well-chosen paints are used. Fairly early on, some manufacturers put printed numbers on as an additional identifying aid. Some might say the system is poorly designed, as it would be simple enough to choose ten colors that work for most color blind people.

Color bands were used because they were easily and cheaply printed on tiny components. However, there were drawbacks, especially for color blind people. Overheating of a component or dirt accumulation may make it impossible to distinguish brown from red or orange. Advances in printing technology have now made printed numbers more practical on small components. The values of components in many surface mount packages are marked with printed alphanumeric codes instead of a color code.

Resistors

One decade of the E12 series (there are twelve preferred values per decade of values) shown with their electronic color codes on resistors

A 0 Ω resistor (zero ohm), marked with a single black band

Color band system

To distinguish left from right there is a gap between the C and D bands:

1. The first significant figure of component value (left side)
2. The second significant figure (some precision resistors have a third significant figure, and thus five bands).
3. The decimal multiplier (number of trailing zeroes, or power of 10 multiplier)
4. If present, indicates tolerance of value in percent (no band means 20%)

In the above example, a resistor with bands of red, violet, green, and gold has first digit 2 (red; see table below), second digit 7 (violet), followed by 5 (green) zeroes: 2700000 ohms. Gold signifies that the tolerance is ±5%.

Precision resistors may be marked with a five band system, to include three significant digits, a power of 10 multiplier (number of trailing zeroes, and a tolerance band. An extra-wide first band indicates a wire-wound resistor.

Resistor color code

Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-HDBK-199 for further details.

Tight tolerance resistors may have three bands for significant figures rather than two, or an additional band indicating temperature coefficient of resistance (TCR), in units of ppm/K.

All coded components have at least two value bands and a multiplier; other bands are optional.

The standard color code per IEC 60062:2016 is as follows:

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Resistors use various E series of preferred numbers for their specific values, which are determined by their tolerance. These values repeat for every decade of magnitude: ... 0.68, 6.8, 68, 680, ... For resistors of 20% tolerance the E6 series, with six values: 10, 15, 22, 33, 47, 68, then 100, 150, ... is used; each value is approximately the previous value multiplied by ⁶√10. For 10% tolerance resistors the E12 series, with ¹²√10 as multiplier, is used; similar schemes up to E192, for 0.5% or tighter tolerance are used. The separation between the values is related to the tolerance so that adjacent values at the extremes of tolerance approximately just overlap; for example, in the E6 series 10 + 20% is 12, while 15 − 20% is also 12.

Zero ohm resistors, marked with a single black band, are lengths of wire wrapped in a resistor-like body which can be mounted on a printed-circuit board (PCB) by automatic component-insertion equipment. They are typically used on PCBs as insulating "bridges" where two tracks would otherwise cross, or as soldered-in jumper wires for setting configurations.

Body-end-dot system

The "body-end-dot" or "body-tip-spot" system was used for cylindrical composition resistors sometimes still found in very old equipment (built before the Second World War); the first band was given by the body color, the second band by the color of one end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was in the body color, silver, or gold for 20%, 10%, 5% tolerance (tighter tolerances were not routinely used).

Examples

Example color-coded resistors

From top to bottom:

• Green, blue, black, black, brown
  • 560 ohms ±1%
• Red, red, orange, gold
  • 22000 ohms ±5%
• Yellow, violet, brown, gold
  • 470 ohms ±5%
• Blue, grey, black, gold
  • 68 ohms ±5%

The physical size of a resistor is indicative of the power it can dissipate.

There is an important difference between the use of three and of four bands to indicate resistance. The same resistance is encoded by:

• Red, red, orange = 22 followed by 3 zeroes = 22000 (excluding default, silver, or gold tolerance)
• Red, red, black, red = 220 followed by 2 zeroes = 22000 (excluding brown or other band for tolerance)

Mnemonics

Further information: List of electronic color code mnemonics

Useful mnemonics have been created to make it easier to remember the numeric order of resistor color bands:

• Betty Brown Runs Over Your Garden But Violet Gingerly Walks.
• Bad Bears Raid Our Yummy Grub But Veto Grey Waffles.
• BB ROY from Great Britain has a Very Good Wife.

The following example includes the tolerance codes — gold, silver and none:

• Bad Beer Rots Out Your Guts But Vodka Goes Well – Get Some Now.

The colors are sorted in ascending order of visible light photon frequency/energy like in a rainbow to make them easy to remember and to reduce the significance of possible read errors due to color shifts and fading over time: red (2), orange (3), yellow (4), green (5), blue (6), violet (7). Black (0) has no energy, brown (1) has a little more, white (9) has everything and grey (8) is like white, but less intense.

Capacitors

Capacitors may be marked with 4 or more colored bands or dots. The colors encode the first and second most significant digits of the value in picofarads, and the third color the decimal multiplier. Additional bands have meanings which may vary from one type to another. Low-tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually, but not always, possible to work out what scheme is used by the particular colors used. Cylindrical capacitors marked with bands may look like resistors.

Color		Significant digits	Multiplier	Tolerance (%)	Characteristic	DC working voltage (V)	Operating temperature (°C)	EIA/vibration (Hz)
	Black	0	1	—	—	—	−55 to +70	10 to 55
	Brown	1	10	±1	B	100	—	—
	Red	2	100	±2	C	—	−55 to +85	—
	Orange	3	1000	—	D	300	—	—
	Yellow	4	10000	—	E	—	−55 to +125	10 to 2000
	Green	5	100000	±0.5	F	500	—	—
	Blue	6	1000000	—	—	—	−55 to +150	—
	Violet	7	10000000	—	—	—	—	—
	Grey	8	—	—	—	—	—	—
	White	9	—	—	—	—	—	EIA
	Gold	—	—	±5	—	1000	—	—
	Silver	—	—	±10	—	—	—	—

Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics. A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.

Polyester film and "gum drop" tantalum electrolytic capacitors may also be color-coded to give the value, working voltage and tolerance.

Postage stamp capacitors and war standard coding

Postage-stamp mica capacitors marked with the EIA 3-dot and 6-dot color codes, giving capacitance value, tolerance, working voltage, and temperature characteristic. This style of capacitor was used in vacuum-tube equipment.

Capacitors of the rectangular "postage stamp" form made for military use during World War II used American War Standard (AWS) or Joint Army-Navy (JAN) coding in six dots stamped on the capacitor. An arrow on the top row of dots pointed to the right, indicating the reading order. From left to right the top dots were: either black, indicating JAN mica, or silver, indicating AWS paper; first significant digit; and second significant digit. The bottom three dots indicated temperature characteristic, tolerance, and decimal multiplier. The characteristic was black for ±1000 ppm/°C, brown for ±500, red for ±200, orange for ±100, yellow for −20 to +100 ppm/°C, and green for 0 to +70 ppm/°C.

A similar six-dot code by EIA had the top row as first, second and third significant digits and the bottom row as voltage rating (in hundreds of volts; no color indicated 500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance capacitors, and the dots signified first and second significant digits and the multiplier. Such capacitors were common in vacuum tube equipment and in surplus for a generation after the war but are unavailable now.

Inductors

Standards IEC 60062 / EN 60062 do not define a color code for inductors, but manufacturers of small inductors use the resistor color code, typically encoding inductance in microhenries. A white tolerance ring is used by TDK to indicate custom specifications.

Diodes

The part number for small JEDEC "1N"-coded diodes – in the form "1N4148" – is sometimes encoded as three or four rings in the standard color code, omitting the "1N" prefix. The 1N4148 would then be coded as yellow (4), brown (1), yellow (4), grey (8).

Wire

Transformer

Power transformers used in North American vacuum-tube equipment were often color-coded to identify the leads. Black was the primary connection, red secondary for the B+ (plate voltage), red with a yellow tracer was the center tap for the B+ full-wave rectifier winding, green or brown was the heater voltage for all tubes, yellow was the filament voltage for the rectifier tube (often a different voltage than other tube heaters). Two wires of each color were provided for each circuit, and phasing was not identified by the color code.

Audio transformers for vacuum tube equipment were coded blue for the finishing lead of the primary, red for the B+ lead of the primary, brown for a primary center tap, green for the finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped secondary. Each lead had a different color since relative polarity or phase was more important for these transformers. Intermediate-frequency tuned transformers were coded blue and red for the primary and green and black for the secondary.

Other

Wires may be color-coded to identify their function, voltage class, polarity, phase or to identify the circuit in which they are used. The insulation of the wire may be solidly colored, or where more combinations are needed, one or two tracer stripes may be added. Some wiring color codes are set by national regulations, but often a color code is specific to a manufacturer or industry.

Building wiring under the US National Electrical Code and the Canadian Electrical Code is identified by colors to show energized, neutral, and grounding conductors, and to identify phases. Other color codes are used in the UK and other areas to identify building wiring or flexible cable wiring.

Mains electrical wiring, both in a building and on equipment, was once usually red for live, black for neutral, and green for earth, but this was changed as it was a hazard for color-blind people, who might confuse red and green; different countries use different conventions. Red and black are frequently used for positive and negative of battery or other single-voltage DC wiring.

Thermocouple wires and extension cables are identified by color code for the type of thermocouple; interchanging thermocouples with unsuitable extension wires destroys the accuracy of the measurement.

Automotive wiring is color-coded but standards vary by manufacturer; differing SAE and DIN standards exist.

Modern personal computer peripheral cables and connectors are color-coded to simplify connection of speakers, microphones, mice, keyboards and other peripherals, usually according to coloring schemes following recommendations such as PC System Design Guide, PoweredUSB, ATX, etc.

A common convention for wiring systems in industrial buildings is: black jacket – AC less than 1,000 volts, blue jacket – DC or communications, orange jacket – medium voltage 2,300 or 4,160 V, red jacket 13,800 V or higher. Red-jacketed cable is also used for relatively low-voltage fire alarm wiring, but has a much different appearance.

Local area network cables may also have non-standardised jacket colors identifying, for example, process control network vs. office automation networks, or to identify redundant network connections, but these codes vary by organization and facility.

See also

• E series of preferred numbers (IEC 60063) – series of preferred resistance and capacitance values
• Color code
• Electrical wiring – AC power wiring inside buildings, including standard color codes

External links

Online resistor calculators

• Multi-purpose resistor code converter (4 and 5 band, mobile-friendly, shows nearest standard value)
• 6 band resistor color code calculator (easy lookup, 4 and 5 band calculators also available)

Historical charts

• Wheel charts
• Reference charts