Decoding the Color Bands on Resistors: A Comprehensive Guide

Anyone working with circuit boards needs to know how to read resistors’ resistance values to prevent errors such as burned-out LEDs or microprocessor overheating.

Today, color codes on resistors follow the international standard in IEC 60062, but that wasn’t always the case. In the 1920s and 1930s, companies such as the RMA (Radio Manufacturer’s Association) used their own color codes on resistors. The first standardization occurred in 1952. It was meant to be only for fixed resistors but soon grew to encompass color code standards for capacitors.

It isn’t a perfect system. Color codes don’t account for color-blind people; and burned-out resistors can lose their color. Whereas color coding began because it was easy to print colors on resistors, today, it’s possible to print alphanumeric characters on even tiny resistors.

But the color-coding system is still widely used, and anyone tinkering with electronics should know what the different bands and colors mean.

What resistance color codes tell us

Resistance color codes tell us more than just the resistance. They also convey information on the resistor’s tolerance and temperature coefficient. Military resistors also have a failure rate band to specify how often the resistor fails, but this band isn’t used much in commercial electronics, so we won’t be looking at it in this tutorial.

Resistors can have between three and six color bands, with higher numbers being more precise. The pattern you’ll see most often is the four-band pattern.

How to read resistor color codes

The colors represent different values depending on their positions. This is best understood in a chart.

First, second, and third bands

The first and second bands always represent a digit in the resistor’s ohm value, regardless of the number of bands.

The third band represents the multiplier if the resistor has three or four bands, but it represents a digit if the resistor has five or more bands.

Let’s look at some examples:

Ohm multiplier band

For three- and four-band resistors, the third band is the multiplier. It multiplies the value of the preceding digits by anything from megaohms to milliohms.

The fourth band becomes the multiplier in resistors with five bands or more.

Tolerance band

Resistor tolerance is represented as a percentage using the symbol “±.” This symbol means that the resistance can vary either up (+) or down (-) from the specified value by the tolerance percentage.

For example, if a resistor has a resistance of 750Ω with a tolerance of 2%, then the tolerance value is 15Ω (750 * 2%) either up or down. So, that resistor would have a resistance of anything between 735Ω and 765Ω.

Temperature coefficient

The temperature coefficient can also be called the reliability band. It exists only on six-band resistors. It’s measured in ppm/K.

Ppm/K means parts per million per Kelvin. The Kelvin scale increments use the same gradation as the Celsius scale, so the temperature coefficient band measures how much the resistor’s value will change per Celsius/Kelvin degree up or down.

For example, if we convert ppm/K to a decimal value, we get 0.0001 [100 * 10^(-6)]. Therefore, a resistor of 100Ω will change by 0.01% for every degree up or down (100Ω * 0.0001).

Next steps

Well done, you now know how to read resistor color codes! The next step is to memorize the codes. Various mnemonics exist for this, and a quick search will give you some that might help, or you can create your own.

You can also save this page for easy reference whenever you face a resistor whose codes you must decipher.

And, if you have any questions, you can also reach out to us for help.

(Note: This post is for educational purposes only and should not be used as a substitute for professional advice. Always consult with a qualified professional or expert when dealing with electrical components.)

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