Electronic Color Code

The electronic colour code is a long-standing system used to indicate the electrical values, tolerances and ratings of electronic components. While most associated with resistors, it is also applied to capacitors, inductors, diodes and legacy wiring systems. The code represents numerical information using coloured bands or dots printed directly onto components, a method originally chosen because it was inexpensive and easy to apply to miniature parts. Although modern components increasingly use alphanumeric marking, the colour code remains widely taught and encountered in through-hole components.

Historical Development

Before standardisation, manufacturers employed their own methods for marking component values, creating inconsistency across early electronic equipment. In the 1920s, the Radio Manufacturers Association introduced a unified resistor colour code to simplify identification. The scheme was adopted in commercial radio receivers from 1930 onwards, and its governing organisation later appeared under names such as RTMA, RETMA and the Electronic Industries Alliance.
International standardisation followed in 1952 with IEC 62-1952, which subsequently expanded to include capacitors. National standards such as DIN 40825, BS 1852 and IS 8186 adopted the system, and it is now defined in IEC 60062 (2016). Alongside colour bands, the standards also describe the RKM alphanumeric code used for modern resistors and capacitors.
Advances in printing technology have made numeric codes more practical, especially for surface-mount components. However, colour bands are still common in through-hole resistors and certain capacitors, while older equipment may use systems no longer manufactured.

Resistor Colour-Band System

Resistors most commonly use a four-band system. Two bands indicate significant digits, the third the multiplier (power of ten) and the fourth the tolerance. For example, red–violet–green–gold corresponds to:

• Red (2)
• Violet (7)
• Green (×10⁵ multiplier)
• Gold (±5% tolerance)

Precision resistors may use a five-band system, adding a third significant digit. Military resistors may include a reliability band, while high-accuracy components may show another band for the temperature coefficient of resistance. All components marked by colour code include at least two significant-value bands and a multiplier; additional information is optional.
Preferred resistor values follow the E-series (E6, E12, up to E192), providing standardised sets of values matched to tolerance ranges. Wider tolerances use fewer preferred values per decade; narrower tolerances require finer resolution. Zero-ohm resistors, used as PCB jumpers, are marked by a single black band.

Body–End–Dot System

A predecessor to the modern band arrangement, the body–end–dot system appeared on pre-Second World War cylindrical resistors. The resistor’s body colour gave the first digit, one end indicated the second, and a central dot or ring showed the multiplier. The remaining end colour often indicated tolerance. These resistors survive mainly in vintage equipment.

Examples and Interpretation

Typical examples include:

• Green–blue–black–black–brown: 560 Ω, ±1%
• Red–red–orange–gold: 5.6 kΩ, ±5%
• Yellow–violet–brown–gold: 470 Ω, ±5%
• Blue–grey–black–gold: 68 Ω, ±5%

The physical size of through-hole resistors corresponds to their power rating, independent of the colour code itself. A key distinction exists between components using three significant-figure bands and those using two; both can represent the same numerical resistance value when different orders of magnitude are applied.

Mnemonics

Numerous mnemonics help memorise the digit sequence black (0), brown (1), red (2), orange (3), yellow (4), green (5), blue (6), violet (7), grey (8) and white (9). Many include tolerance indicators such as gold, silver and “none” to assist with rapid identification. These mnemonic sequences correspond to ascending wavelengths across the visible spectrum, providing a natural ordering to reduce reading errors.

Capacitor Colour Codes

Capacitors may use bands or dots similar to resistors, though variations exist between types. For band-marked cylindrical capacitors, the first two colours typically represent significant digits and the third the multiplier in picofarads. Additional bands may indicate voltage rating or temperature characteristics.
Older paper and ceramic capacitors sometimes used a wide black band to mark the outer electrode, which could be connected to chassis ground to reduce noise. Polyester film and “gum-drop” tantalum capacitors may also use colour coding to denote capacitance, working voltage and tolerance.
During the Second World War, military equipment commonly employed capacitors with EIA, AWS or JAN coding systems using three or six dots. The marked dots indicated significant digits, temperature characteristics, tolerance and voltage rating, with the reading direction shown by an arrow.