Resistor Color Code Identification

  While these codes are most often  associated with resistors, then can also apply to capacitors and other  components.
  The standard color coding method for resistors  uses a different color to represent each number 0 to 9: black, brown, red,  orange, yellow, green, blue, purple, grey, white. On a 4 band resistor, the  first two bands represent the significant digits. On a 5 and 6 band, the first  three bands are the significant digits. The next band represents the multiplier  or "decade". As in the above 4 band example, the first two bands are red and  purple, representing 2 and 7. The third band is orange, representing 3 meaning  10³or 1000. This gives a value of 27 * 1000, or 27000 Ohms. The gold  and silver decade bands divide by a power of 10, allowing for values below 10  Ohms. The 5 and 6 band resistors work exactly the same as the 4 band resistor.  They just add one more significant digit. The band after the decade is the  tolerance. This tells how accurate the resistance compared to its specification.  The 4 band resistor has a gold tolerance, or 5%, meaning that the true value of  the resistor could be 5% more or less than 27000 Ohms, allowing values between  25650 to 28350 Ohms. The last band on a 6 band resistor is the temperature  coefficient of the resistor, measured in PPM/C or parts per million per degree  Centigrade. Brown (100 PPM/C) are the most popular, and will work for most  reasonable temperature conditions. The others are specially designed for  temperature critical applications.

Alpha-Numeric Code Identification

With the sizes of resistors and  other components shrinking or changing in shape, it is getting difficult to fit  all of the color bands on a resistor. Therefore, a simpler alphanumeric coding  system is used. This method uses three numbers, sometimes followed by a single  letter. The numbers represent the same as the first three bands on a 4 band  resistor. On the above SIL network, the 4 and 7 are the significant digits and  the 3 is the decade, giving 47 x 1000 or 47000 Ohms. The letter after the  numbers is the tolerance. The different representations are: M=±20%, K=±10%,  J=±5%, G=±2%, F=±1%.

  To simplify the writing of large  resistor values, the abbreviations K and M are used for one thousand and one  million. To keep the convention standard, R is used to represent 0. Because of  problems in seeing the decimal point in some printed texts, the 3 letters: K M  or R are used in place of the decimal point. Thus, a 2,700 Ohm resistor is  written 2K7 and a 6.8 Ohm resistor is written 6R8.

  These identify a range of resistors  that are know as "preferred values". In the E12 range there are 12 "preferred"  or "basic" resistor values, and all of the others are simply decades of these  values:

The table below lists every resistor value of the E12  range of preferred values. You will notice that there are 12 rows containing the  basic resistor values, and the columns list the decade values thereof. This  range most commonly covers standard carbon film resistors, which are not readily  available in values above 10 Megohms - 10M (10 Million Ohms)

The E24 range of preferred values includes all of the E12 values, plus a  further 12 to enable the selection of more precise resistances. In the E24 range  the preferred values are:

The  table below lists every resistor value of the E24 range of preferred values. You  will notice that there are 24 rows containing the basic resistor values and the  columns to the right list the decade values thereof. This range most commonly  covers metal film resistors which are not readily available in values above 1  Megohm - 1M0.

There are also E48  and E96 tables, which have even more values. Resistors in these groups are less  common and tend to have a better tolerance rating.   The table  below shows the color codes for the E12 and E24 preferred values. Notice how the  first two colors in each row are the same, and the last color in each column is  the same. Each column is a decade, and each row in that column is a different  one of the E24 values.