# Resistor Values

## Standard Resistor Values

In 1952, the IEC (International Electrotechnical Commission) decided to define the resistance and tolerance values into a norm, to ease the mass manufacturing of resistors. These are referred to as "preferred values" or "E-series", and they are published in standard IEC 60063:1963. These standard values are also valid for other components like capacitors, inductors and Zener diodes. The preferred values for resistors were established in 1952, but the concept of the geometric series was previously introduced by army engineer Renard in the 1870s.

The standardization of resistor values serves several important purposes. When manufacturers produce resistors with different resistance values, these end up approximately equally spaced on a logarithmic scale. This helps the supplier to limit the number of different values that have to be produced or kept in stock. By using standard values, resistors from different manufacturers are compatible for the same design, which is favorable for the electrical engineer.

Aside from the preferred values, many other standards related to resistors exist. Example include the standard sizes for resistors and the marking of resistors with color codes or numerical codes. Power ratings of resistors are not defined in a norm, and, therefore, often deviate from the above described series.

## Preferred Values or E-series

To understand the E-series sets of preferred values, we will examine the E12 in detail. E12 means that every decade (0.1-1.0, 1-10, 10-100, etc.) is divided in 12 steps on a logarithmic scale. The size of every step is equal to:

$$10^{(\frac{1}{12})} = 1.21$$

Thus, every value is 21% or 1.21 times higher than the previous value in the series, rounded to whole numbers. Because of this, all resistors with a tolerance of 10% overlap. The series looks as follows: 1– 1.2 – 1.5 – 1.8 – 2.2 – 2.7 – 3.3 – 3.9 – 4.7 – 5.6 – 6.8 – 8.2 – 10 etc. All of these values can be powers of ten (1.2 – 12 – 120, etc.).

While the E12 series is the most common, other series are also available. It is a good practice to specify resistors from a low series when tolerance requirements are not high. The most common series are:

• E6     20% tolerance
• E12   10%
• E24   5% (also available with 1%)
• E48   2%
• E96   1%
• E192 0.5% (also used for resistors with 0.25% and 0.1%).

## E6 series (tolerance 20%)

10 15 22 33 47 68

The E6 series has six values in each decade. The tolerance is ±20%.

## E12 series (tolerance 10%)

10 12 15 18 22 27
33 39 47 56 68 82

The E12 series is probably the most common series and is available for almost every resistor type. The tolerance is ±10%.

The E12 series resistors with their color codes

## E24 series (tolerance 5% and 1%)

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 (tolerance 2%)

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

Each decade is divided into 48 values. A third significant digit is added (just as for the E96 and E192 series).

## E96 series (tolerance 1%)

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
487 499 511 523 536 549
562 576 590 604 619 634
649 665 681 698 715 732
750 768 787 806 825 845
866 887 909 931 953 976

## E192 series (tolerance 0.5%, 0.25% and 0.1%)

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