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The Color Code

To the right is an image of a ½-watt resistor. Due to variations in monitor resolution, it may not be precisely to scale, but it is close enough to make the point. You can see that there are four colored stripes painted around the body of this resistor, and that they are grouped closer to one end (the top) than to the other. To someone who knows the color code, these stripes are enough to identify this as a 470Ω, 5% resistor. Imagine putting all of that in numbers on something that small! Or worse, on a ¼-watt resistor, which is even smaller.

The use of colored stripes, or bands, allows small components to be accurately marked in a way that can be read at a glance, without difficulty or any great possibility of error. In addition, the stripes are easy to paint onto the body of the resistor, and so do not add unreasonably to the cost of manufacturing the resistors.

Starting with the color band or stripe closest to one end of the resistor, the bands have the following significance: The first two bands give the two significant digits of the resistance value. The third gives a decimal multiplier which is some power of 10, and generally simply defines how many zeroes to add after the significant digits. The fourth band identifies the tolerance rating of the resistor. If the fourth band is missing, it indicates the original default tolerance of 20%. The bands may take on colors according to the following figure and table:

Color Significant Digits Multiplier (1 and 2) (3) 0 1 1 10 2 100 3 1000 4 10,000 5 100,000 6 1,000,000 7 8 9 0.1 5% 0.01 10% 20%

Standard resistors may be obtained in values ranging from 0.24Ω to 22 Megohms (22,000,000Ω). However, they are not available in just any value; only the following combinations of first and second significant digits are used:

 10 * 12 15 * 18 22 * 27 33 * 39 47 * 56 68 * 82 11 13 16 20 24 30 36 43 51 62 75 91

All values above may be obtained in 5% tolerance, while the boldface entries are available in 10% tolerance. Only the ones marked with an asterisk (*) are available in 20% tolerance, and you probably won't be able to find even them on today's market.

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