Resistors are electrical components that we will use quite often. Quite simply they resist the flow of electricity. We will spend more time talking about why we might want to do this in a future lesson. For now we need to focus on how we identify them. It would be convenient if the numerical value was printed on the side of resistors. Unfortunately that’s not what they do. Instead, the value of a resistor must be determined using the colored bands that wrap around them.

Various ResistorsWe will focus on four banded resistors, but it should be noted that there are resistors with more than four bands as well. If you find resistors in older electronic devices they may only have three bands, but this is very uncommon today.

The fourth band on almost all resistors made today is gold. If your resistor has gold for the first band simply turn the resistor around so it’s the fourth. The fourth band indicates the tolerance. Gold means ±5%. So if the other colors tell us the resistor has a value of 100 ohms, then the true value will lie between 95 and 105 ohms. If the fourth band is silver then it is ±10%.

The first band is the first digit in the resistors value. The second band is the second digit. The third band is the multiplier, but I choose to think of this as the number of zeros to tack on. So, using the conventional way of thinking about it, if you have a resistor with Brown, Black, Red, Gold bands then the first digit of the number would be one, the second number would be zero, the multiplier would be 100, with a tolerance of ±5%. So, 10 x 100 = 1,000 ohms ±5%.

Conventional Color Code

 Color  1st Digit  2nd Digit  Multiplier
 Black  0 0  1
 Brown  1  1  10
 Red  2  2 100
 Orange  3  3 1,000
 Yellow  4  4 10,000
 Green  5  5 100,000
 Blue  6  6 1,000,000
 Violet  7  7
 Grey  8  8
 White 9  9

Alternative way of thinking

I instead prefer to think about the third band not as a multiplier, but instead as the number of zeros to tack on. Using only the table below. If you have a resistor with Brown, Black, Red, Gold bands then the first digit 1, second digit 0, then tack on 2 zeros for a value of 1,000 ohms ±5%.

 Color  Value
 Black  0
 Brown  1
 Red  2
 Orange  3
 Yellow  4
 Green  5
 Blue  6
 Violet  7
 Grey  8
 White 9

There a couple ways to remember the order the colors go in. First off you might notice that the color portion closely matches the order of colors in the rainbow, “Roy G. Biv”. It simply lacks the indigo. There are also a number of different mnemonics for remembering the order . One is, “Better be right or your great big venture goes wrong.”

 Color  Mnemonic
 Black  Better
 Brown Be
 Red  Right
 Orange  Or
 Yellow  Your
 Green  Great
 Blue  Big
 Violet  Venture
 Grey  Goes
 White Wrong