Electronics Handbook/Component Identification

4-band axial resistors


For example, if you are looking for a 12K (12000 ohm) resistor with ±5% tolerance, you would be looking for a Brown (1) Red (2) Orange (×103) Gold (±5%) resistor.

12×103 ohm = 12000 Ω = 12 kΩ

Note that red to violet are the colors of the rainbow where red is low energy and violet is higher energy. Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent, 6.8, 68, 680. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colors, which you will learn to recognize without checking a chart. To help you remember them, the standard values for 10% resistors are:

1 0
1 2
1 5
1 8
2 2
2 7
3 3
3 9
4 7
5 6
6 8
8 2

SMD/SMT resistors


SMD (surface mounted device) or SMT (surface mount technology; same thing) resistors are found mostly on devices where large scale integration is present. They generally use an alphanumeric numbering system.

For surface mount resistors, a numerical code is used. For 10% tolerance resistors, 3 numbers are used, for 1% resistors, 4 digits are used. The scheme is similar to color codes, in that the first two or three digits are the significant digits, and the last digit is the multiplier (expressed as an exponent of 10). This is easy to remember as "the first digits then as many zeros as the last digit after it" ohms. "683" for instance, represents 68 with three zeros after it: 68 000 = 68 kΩ. Likewise, "4991" represents 499 with 1 zero after it: 499 0 = 4.99 kΩ.

For small resistance values, an alternate notation is often used. For these, an R is used in place of the decimal. For example, 5R6 = 5.6 Ω.

They are small.

Large resistors


For large power resistors and potentiometers, the value is usually written out implicitly as "10 kΩ", for instance.



In the top example, the colors are brown (1) - black (0) - orange (×103) - gold (5%). This means 1 0 ×103 Ω ± 5% = 10 ± 0.5 kΩ. This resistor has a value anywhere from 9.5 to 10.5 kΩ

The second example has 5 stripes. They are brown (1) - black (0) - black (0) - red (×102) - brown (1%). This means 1 0 0 ×102 Ω ± 1% = 10 ± 0.1 kΩ. This resistor then has a value anywhere from 9.9 to 10.1 kΩ.

Note that these are both 10 kΩ.

The third example is a larger power resistor, and is labeled green (5) - blue (6) - black (×100) - gold (5%). This means 5 6 ×100 Ω ± 5% = 56 ± 2.8 Ω. This resistor then has a value anywhere from 53.2 to 58.8 Ω. It has a higher power rating than the others, which is not labeled, but is obvious from its larger size.

SMD/SMT capacitors


These are often not even labeled. If they are labeled, it is the same system as SMT resistors, but representing pF. Polarized capacitors are marked with a stripe on the positive end of the package, though some electrolytic SMT capacitors are marked on the negative end of the package. They are rectangular, and often black or tan colored. The black capacitors are easily mistaken for diodes due to the white stripe on one end...



External resources:

Sometimes the value of an inductor is printed directly on it. If no units are given, µH can be assumed. If it looks like the system used by SMT resistors, it is probably that system, except that the value represented is in µH.

Axial inductors


If an inductor uses the color code system, the value represented is in µH. Expect to see a wide silver or gold band before the normal colored bands, and a thin tolerance band at the end. but have some more information that is not given.