Why is a color code used for resistors?

There are many different types of Resistors available which can be used in both electrical and electronic circuits to control the flow of current or to produce a voltage drop in many different ways. But to do this, the actual resistor needs to have some form of “resistive” or “resistance” value. Resistors are available in a range of different resistance values from fractions of an Ohm ( Ω ) to millions of Ohms.

Obviously, it would be impractical to have available resistors of every possible value, for example, 1Ω, 2Ω, 3Ω, 4Ω, etc, because literally tens of hundreds of thousands, if not tens of millions of different resistors would need to exist to cover all the possible values. Instead, resistors are manufactured in what are called “preferred values” with their resistance value printed onto their body in colored ink.

The resistance value, tolerance, and wattage rating are generally printed onto the body of the resistor as numbers or letters when the body of the resistor is big enough to read the print, such as large power resistors. But when the resistor is small such as a 1/4 watt carbon or film type, these specifications must be shown in some other manner as the print would be too small to read.

So to overcome this, small resistors use colored painted bands to indicate both their resistive value and their tolerance with the physical size of the resistor indicating its wattage rating. These colored painted bands produce a system of identification generally known as a Resistors Colour Code.

An international and universally accepted resistor color code scheme was developed many years ago as a simple and quick way of identifying a resistor ohmic value no matter what its size or condition. It consists of a set of individual colored rings or bands in spectral order representing each digit of the value of the resistor.

The resistor color code markings are always read one band at a time starting from the left to the right, with the larger width tolerance band oriented to the right side indicating its tolerance. By matching the color of the first band with its associated number in the digit column of the color chart below the first digit is identified and this represents the first digit of the resistance value.

Again, by matching the color of the second band with its associated number in the digit column of the color chart we get the second digit of the resistance value and so on. Then the resistor color code is read from left to right as illustrated below:

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