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 already 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 of 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. An example is standard sizes for resistors, or the marking of resistors with color codes or numerical codes. Power ratings of resistors are not defined in a norm, therefore often is deviated from the above described series.

Preferred values or E-series

As basis the E12 has been developed. E12 means that every decade (0.1-1, 1-10, 10-100 etc) is divided in 12 steps. The size of every step is equal to:

Formula for preferred values for resistors 10^(1/12)=1.21

 

One could also say every value is 120% higher than the last, 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 these values can be powers of ten (1.2– 12 – 120 etc).

One decade of the E12 series

Next to the E12 series, other series are existing. It is a good practise to specify resistors from a low series when tolerance requirements are not high. The most common series are:

  • E6   20%
  • 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%)

101522334768

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

E12 series (tolerance 10%)

101215182227
333947566882

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

resistor standard values E12

The E12 series of resistor values, including their color codes.

 

E24 series (tolerance 5% and 1%)

101112131516
182022242730
333639434751
566268758291

 

E48 series (tolerance 2%)

100105110115121127
133140147154162169
178187196205215226
237249261274287301
316332348365383402
422442464487511536
562590619649681715
750787825866909953

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

E96 series (tolerance 1%)

100102105107110113
115118121124127130
133137140143147150
164158162165169174
178182187191196200
205210216221236232
237243249255261267
274280287294301309
316324332340348357
365374383392402412
422432442453464475
487491511523536549
562576590604619634
649665681698715732
750768787806825845
866887909931953976

 

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

100101102104105106107109110111113114
115117118120121123124126127129130132
133135137138140142143145147149150152
154156158160162164165167169172174176
178180182184187189191193196198200203
205208210213215218221223226229232234
237240243246249252255258261264267271
274277280284287291294298301305309312
316320324328332336340344348352357361
365370374379383388392397402407412417
422427432437442448453459464470475481
487493499505511517523530536542549556
562569576583590597604612619626634642
649657665673681690698706715723732741
750759768777787796806816825835845856
866876887898909920931942953965976988