Resistor

The color code on a resistor can tell you a lot of information about the resistor, but you have to know how to read it first. So, how do you turn a bunch of colored lines on a resistor into numbers? Read on to find out.

Resistors are measured in a unit called Ohms, named after a German physicist name George Ohm. Ohms are represented by the Ω symbol, the uppercase greek letter omega. Throughout this guide we'll use Ω to mean ohm so you get used to seeing it and reading it.

The first step is to take a look at what the colors mean. Each color has a number associated with it. These numbers are listed below.

  • 0 - Black
  • 1 - Brown
  • 2 - Red
  • 3 - Orange
  • 4 - Yellow
  • 5 - Green
  • 6 - Blue
  • 7 - Violet
  • 8 - Grey
  • 9 - White
  • 10% - Silver
  • 5% - Gold

Next we need to understand the code. Most resistors have 4 bands printed onto them. The first three numbers tell you what the resistance of the resistor is in ohms. The fourth band is a tolerance band.

The first three bands use a system very similar to scientific notation. The first two bands are a numerical value, and the third band is a multiplier. For example, If the resistor color code is Red Green Orange, the value of the resistor is 25 x 103, or 25000 Ohms. For simplicity resistors usually use a set of standard abbreviations. 25000 Ohms would be called 25 Kilo-Ohms, or KΩ.

Now for the tolerance band. In most of the resistors that you will see, the tolerance band will be either gold or silver. Taking our previous example, if the resistor has the colors Red Greed Orange Gold, then the resistor is a 25KΩ resistor with a 5% tolerance. This means that if you measure the resistor with an ohmmeter, it will be somewhere in between 23,750Ω and 26,250Ω.

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