Electronic color code

The electronic color code is used to indicate the values or ratings of electronic components, very commonly for resistors, but also for capacitors, inductors, and others.

The electronic color code was developed in the early 1920s by the Radio Manufacturer's Association, now part of Electronic Industries Alliance and was published as EIA-RS-279. The current international standard is IEC 60062.

Colorbands were commonly used (especially on resistors) because they were easily printed on tiny components, decreasing construction costs. However, there were drawbacks, especially for color blind]] people.

Today, printed numbers are being used in favor of colorbands (see Other schemes below).

Other schemes
Color-coding of this form is becoming rarer. In newer equipment, most passive components come in surface mount packages. Many of these packages are unlabeled, and those that are normally use alphanumeric codes, not colors.

In one popular marking method, the manufacturer prints 3 digits on components: 2 value digits followed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 Ω, a capacitor marked 104 is 100 nF (10x104 pF), and an inductor marked 475 is 4.7 mH (4,700,000 nH). This can be confusing; a resistor marked 100 might seem to be a 100 Ω unit, and we must rely upon experience to interpret the marking as 10 Ω (10×100). Another way is to use the "kilo-" or "mega-" prefixes in place of the decimal point:

1K2 = 1.2 kΩ = 1,200 Ω 4M7 = 4.7 MΩ = 4,700,000 Ω 6R8 = 6.8 Ω

For 1% resistors, a three-digit alphanumeric code is sometimes used, which is not obviously related to the value but can be derived from a table of 1% values. For instance, a resistor marked 68C is 499(68) × 100(C) = 49,900 Ω. In this case the value 499 is the 68th entry of a table of 1% values between 100 and 999.

It is sometimes not obvious whether a color coded component is a resistor, capacitor, or inductor, and this may be deduced by knowledge of its circuit function, physical shape or by measurement (capacitors have nearly infinite resistance; unfortunately, so do faulty open-circuit resistors and inductors).

Resistor, capacitor and inductor
shown with their electronic color codes on resistors.]]

Resistor values are always coded in ohms, capacitors in picofarads (pF), inductors in microhenries (µH), and transformers in volts.

* band A is first significant figure of component value * band B is the second significant figure * band C is the decimal multiplier * band D if present, indicates tolerance of value in percent (no color means 20%)

For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.

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, and/or an additional band indicating temperature coefficient, in units of ppm/K.

All coded components will have at least two value bands and a multiplier; other bands are optional (italicised below).

The Standard EIA Color Code Table per EIA-RS-279 is as follows:



Note: red to violet are the colors of the rainbow where red is low energy and violet is higher energy.

As an example, let us take a resistor which (read left to right) displays the colors yellow, violet, yellow, brown. We take the first two bands as the value, giving us 4, 7. Then the third band, another yellow, gives us the multiplier 104. Our total value is then 47 x 104 Ω, totalling 470,000 Ω or 470 kΩ. Our brown is then a tolerance of ±1%.

Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent; 6.8, 68, 680, and so forth. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colors, which make them easier to understand.

A much older resistor color coding scheme, still to be found on components in vintage radios, is known as 'body-tip-spot'. Here the color of the resistor body was the first digit, the color of one tip or end of the resistor was the second, and the color of the spot on the body was the multiplier.