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I f you have just purchased a resistor, it will generally come with some sort of label, but that doesnt help if you find your resistor sitting unaccompanied on a table or in your parts box. Fortunately, every resistor has a set of color bands printed on its casing that tells you the value of the resistor. While there are resistors with six, three, or even one band, the most commonly found resistors by far have four bands, and we are looking at that type in this appendix.

Lets take a close look at a resistor in . A resistor has two wire leads and a body with color bands on it.

A resistor

Not only do the colors of the bands matter, but also the order in which the colors appear. How do you know what each color means? The first step is to orient your resistor in the correct direction, as shown in . On one side of the resistor, the band color will be either silver or gold. This band should be placed on the right-hand side of the resistor. Look for the silver or gold band on the resistor body and place it on the right-hand side.

Orient your resistor.

Now that your resistor is oriented correctly, you can identify the other color bands on the resistor body. We have labeled the bands in in order. The colors on each band have a particular significance.

Numbering the bands on the resistor

is a standard color chart that all resistors follow. You can find similar charts online. Well go over what each band means in detail. The colors mean the same thing for all resistors.

Resistor band color chart

Now that youve seen the color chart, well show you how to apply it to a resistor.

The first band represents the most significant digit, or the first digit in the number. For example, on our resistor in , the first band is red. Looking at the color chart, you see that red on the first band equates to the number 2.

The first band

The second band signifies the second most significant digit. On this resistor, the second band is also red. As you see in , the chart indicates again that the number 2 is represented by the red color of your second band.

The second band

The first two bands taken together give us the number 22. The first two bands on a resistor will always represent a number between 10 and 99. (Well explain what these numbers mean shortly.) The third digit is a little bit different.

The third band, shown in : the first two digits times the multiplier equals the resistance (in ohms).

The third band

Calculating the value of a resistor

This means that our red-red-brown resistor is a 220-ohm resistor. In fact, all red-red-brown resistors have a value of 220 ohms.

The fourth band of our resistor, , represents the resistors tolerance or possible range of accuracy. With a gold band, the accuracy is plus or minus 5 percent, which means that our resistor could be as high as 231 ohms (2201.05) or as low as 209 (2200.95). (This variation is caused by imperfections in the resistors manufacturing process.)

The fourth band

Since the fourth band is always going to be gold or silver, and these are not colors any of the other bands use, we can always use the fourth band to orient our resistor correctly.

1. Q: Are the band colors universal, and will I have to remember what each color means?
2. A: All resistors use the same standard color codes we have talked about here regardless of the manufacturer. You dont have to memorize them you can easily find the color information online, and there are a number of free smartphone apps for all the platforms.
3. Q: What if the bands are hard to see or they have been painted over or erased?
4. A: If your resistors are missing the color bands, you can always use a multimeter to confirm the resistance value.

1. Q: How accurate do I need to be with my resistors?
2. A: Good question. Hobby electronics and electrical components are not super sensitive to minor variations in resistance. The difference between 209 ohms and 231 ohms is not enough to cause any issue with your LED. However, using a resistor with a much higher rating (double or more) or a much smaller rating (half or less) is enough to cause issues.

Although the four-band resistor is very common, some resistors have a different number of bands. The colors indicate the same numbers in the first three bands, but the tolerance values are calculated differently.

Lets look at another resistor and evaluate its color bands to figure out its total resistance value. The resistor in has the color bands brown, black, orange, and gold.

A resistor with the bands labeled

The first step is to orient the resistor correctly. To do that, make sure that the gold band is on the right-hand side ().

Orienting the resistor

Refer back to to reference the color values. You can always look up the chart whenever you need to calculate a resistance value.

The first band is brown, so we can look at the color chart and know that the first digit is a 1 ().

First band

The next color band on the resistor is black, which makes the second digit a 0 ().