Guide for Tech Beginners - Standard or Common Resistor Values

The Electronic Industries Association (EIA), and other authorities, specify standard values for resistors, sometimes referred to as the "preferred value" system. The preferred value system has its origins in the early years of the last century at a time when most resistors were carbon-graphite with relatively poor manufacturing tolerances. The rationale is simple - select values for components based on the tolerances with which they are able to be manufactured. Using 10% tolerance devices as an example, suppose that the first preferred value is 100 ohms. It makes little sense to produce a 105 ohm resistor since 105 ohms falls within the 10% tolerance range of the 100 ohm resistor. The next reasonable value is 120 ohms because the 100 ohm resistor with a 10% tolerance is expected to have a value somewhere between 900 and 110 ohms. The 120 ohm resistor has a value ranging between 110 and 130 ohms. Following this logic, the preferred values for 10% tolerance resistors between 100 and 1,000 ohms would be 100, 120, 150, 180, 220, 270, 330 and so on (rounded appropriately); this is the E12 series shown in the table below. The EIA "E" series specify the preferred values for various tolerances. The number following the "E" specifies the number of logarithmic steps per decade. The table below is normalized for the decade between 100 and 1,000. The values in any decade can be derived by merely dividing or multiplying the table entries by powers of 10. The series are as follows:

E6 20% tolerance,

E12 10% tolerance,

E24 5% tolerance (and usually 2% tolerance),

E48 2% tolerance,

E96 1% tolerance,

E192 .5, .25, .1% and higher tolerances.

Standard EIA Decade Resistor Values:

E6 series: (20% tolerance) 10, 15, 22, 33, 47, 68

E12 series: (10% tolerance) 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

E24 series: (5% tolerance) 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91

E48 series: (2% tolerance) 100, 105, 110, 115, 121, 127, 133, 140, 147, 154, 162, 169, 178, 187, 196, 205, 215, 226, 237, 249, 261, 274, 287, 301, 316, 332, 348, 365, 383, 402, 422, 442, 464, 487, 511, 536, 562, 590, 619, 649, 681, 715, 750, 787, 825, 866, 909, 953

E96 series: (1% tolerance) 100, 102, 105, 107, 110, 113, 115, 118, 121, 124, 127, 130, 133, 137, 140, 143, 147, 150, 154, 158, 162, 165, 169, 174, 178, 182, 187, 191, 196, 200, 205, 210, 215, 221, 226, 232, 237, 243, 249, 255, 261, 267, 274, 280, 287, 294, 301, 309, 316, 324, 332, 340, 348, 357, 365, 374, 383, 392, 402, 412, 422, 432, 442, 453, 464, 475, 487, 491, 511, 523, 536, 549, 562, 576, 590, 604, 619, 634, 649, 665, 681, 698, 715, 732, 750, 768, 787, 806, 825, 845, 866, 887, 909, 931, 959, 976

E192 series: (0.5, 0.25, 0.1 and 0.05% tolerance) 100, 101, 102, 104, 105, 106, 107, 109, 110, 111, 113, 114, 115, 117, 118, 120, 121, 123, 124, 126, 127, 129, 130, 132, 133, 135, 137, 138, 140, 142, 143, 145, 147, 149, 150, 152, 154, 156, 158, 160, 162, 164, 165, 167, 169, 172, 174, 176, 178, 180, 182, 184, 187, 189, 191, 193, 196, 198, 200, 203, 205, 208, 210, 213, 215, 218, 221, 223, 226, 229, 232, 234, 237, 240, 243, 246, 249, 252, 255, 258, 261, 264, 267, 271, 274, 277, 280, 284, 287, 291, 294, 298, 301, 305, 309, 312, 316, 320, 324, 328, 332, 336, 340, 344, 348, 352, 357, 361, 365, 370, 374, 379, 383, 388, 392, 397, 402, 407, 412, 417, 422, 427, 432, 437, 442, 448, 453, 459, 464, 470, 475, 481, 487, 493, 499, 505, 511, 517, 523, 530, 536, 542, 549, 556, 562, 569, 576, 583, 590, 597, 604, 612, 619, 626, 634, 642, 649, 657, 665, 673, 681, 690, 698, 706, 715, 723, 732, 741, 750, 759, 768, 777, 787, 796, 806, 816, 825, 835, 845, 856, 866, 876, 887, 898, 909, 920, 931, 942, 953, 965, 976, 988

When designing equipment, it is good practice to keep to the lowest E-series section, i.e. it is better to use E6 rather than E12. In this way the number of different parts in any equipment can be minimised. If decade values, i.e. 100R, 1K, 10, etc can be used so much the better. These are very common resistor values and ore widely used. It also reduces the variety of components and makes inventory more manageable.

For many digital designs where the resistor is used as a pull up or pull down, the resistor value is of little consequence and this is easy. For analogue designs it is a little more complicated, and E12, or E24 values are needed. E48, E96 or even E192 series values are needed for high accuracy and close tolerance requirements. As the higher order series are used less, their costs are also normally higher. Using common resistor values can reduce costs as well as reducing inventory.