Enter a value and press Find.
Resistors and capacitors aren't made in every possible value — they come in standard E-series (preferred values) chosen so that, with a given tolerance, the ranges of adjacent values just meet. The number after the E is how many values fill one decade: E12 has 12 values per decade, E24 has 24, and so on. Tighter tolerance uses a denser series.
| Series | Values/decade | Tolerance |
|---|---|---|
| E6 | 6 | ±20% |
| E12 | 12 | ±10% |
| E24 | 24 | ±5% |
| E48 | 48 | ±2% |
| E96 | 96 | ±1% |
When your calculated value isn't a standard one, snap it to the nearest E-series value — or combine two standard resistors in series or parallel to get closer.
The preferred values — 10, 12, 15, 18, 22, 27, 33 and so on — are not arbitrary at all. Each E-series divides every decade into n logarithmically spaced steps, so consecutive values differ by a constant ratio rather than a constant amount:
| Series | Values per decade | Step ratio | Tolerance |
|---|---|---|---|
| E6 | 6 | ×1.468 (46.8%) | ±20% |
| E12 | 12 | ×1.212 (21.2%) | ±10% |
| E24 | 24 | ×1.101 (10.1%) | ±5% |
| E96 | 96 | ×1.024 (2.4%) | ±1% |
Notice how the step ratio always roughly matches twice the tolerance. That is deliberate: the spacing is chosen so that the tolerance bands of neighbouring values just about meet without leaving gaps or overlapping excessively. With ±10% parts on the E12 series, every possible resistance in a decade is covered by some part, and no two values are needlessly redundant.
It also explains why a tighter tolerance needs more values. Buying 1% resistors in the E12 series would be wasteful — you would be paying for precision while still being forced to pick a value up to 10% away from the one you wanted.
Capacitors follow the same system but usually with coarser series, because capacitance tolerances are generally wider and temperature coefficients dominate anyway.
A set of standard "preferred" component values spread logarithmically across each decade, so that with a given tolerance the values cover the whole range without large gaps.
Because tolerance already blurs the exact value. A ±5% resistor covers a range, so only ~24 values per decade (E24) are needed to reach any value within tolerance.
Each value is approximately 10^(k/N) for k = 0…N−1 in a decade, where N is the series number (12, 24, 96…), then rounded to standard printed values.
E6 = ±20%, E12 = ±10%, E24 = ±5%, E48 = ±2%, E96 = ±1%, and E192 = ±0.5% or better.
Pick the nearest, or use a denser series (higher E number), or combine two resistors in series or parallel to get closer — the second tab does this.
Yes — capacitors, inductors, and Zener voltages all use the same preferred-value system, usually E6 or E12 for capacitors.
Combine two standard resistors: in series their values add, in parallel they combine as R1×R2/(R1+R2). This lets you reach almost any target precisely.
Series makes a larger value than either resistor; parallel makes a smaller one. Choose whichever brackets your target, and the calculator finds the closest pair.
How far the standard (or combined) value is from your target, as a percent. Compare it to the resistor tolerance to judge if it matters.
Not necessarily — tighter series (E96/E192) cost more and may be harder to source. Use the loosest series that meets your accuracy need.
Not exactly — the rounding differs slightly, so some E24 values (like 3.3) differ a little from the nearest E96 value. Each series is defined on its own.
Exact odd values may not exist, may be costly, or may have long lead times. Two common resistors are cheap, in stock, and can be more accurate together.
A system of preferred component values in which each decade is divided into a fixed number of logarithmically spaced steps. E12 has twelve values per decade, E24 has twenty-four, and E96 has ninety-six.
Because the values are spaced by a constant ratio rather than a constant amount. For E12 that ratio is the twelfth root of ten, about 1.212, which produces the familiar 10, 12, 15, 18, 22, 27 sequence.
The step ratio is chosen to be roughly twice the tolerance, so adjacent values' tolerance bands just meet. E12 pairs with ±10% parts, E24 with ±5%, and E96 with ±1%.
Use the widest series that meets the requirement. E24 covers most general work; reserve E96 for precision dividers, references and filters where the exact value genuinely matters.
Combine two values in series or parallel, which can land very close to almost any target, or re-examine whether the circuit really needs that precision. In dividers and gain networks the ratio usually matters more than the absolute values.
Yes, but usually coarser ones such as E6 or E12, because capacitance tolerances are typically wider and temperature and voltage coefficients often dominate the error budget anyway.
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