Resistor Color Code and E-Series Calculator
The tolerance band is shown in orange. It is the only band separated from the others, which identifies the reading direction.
Introduction
The resistor color code is not an arbitrary convention: it is a form of scientific notation. The first bands are the significant digits, the next one is the exponent, and the last indicates the tolerance of the preceding digits. Once you see it this way, even six-band resistors become straightforward to read.
The reason some resistor values exist and others do not is explained by the second part of this page: the E series. Standard values are neither random nor uniformly spaced; they follow a geometric progression whose step is related to component tolerance. Knowing which series contains the value you need tells you whether it is a standard part or must be obtained by combining values.
The nominal value is obtained as follows, where \(d_i\) are the band digits and \(m\) is the multiplier exponent:
$$ R = \left(\sum_i d_i \cdot 10^{n-i}\right)\cdot 10^m \qquad R_{\min,\max}=R\,(1\pm t) $$| Bands | Reading | Typical use |
|---|---|---|
| 3 | 2 digits + multiplier | No tolerance band: ±20% is implied |
| 4 | 2 digits + multiplier + tolerance | E12 / E24 series, ±10% and ±5% |
| 5 | 3 digits + multiplier + tolerance | Metal film, E48 / E96 series, ±2% and ±1% |
| 6 | 3 digits + multiplier + tolerance + temperature coefficient | Precision resistors with specified ppm/K |
Card 1 — From color bands to resistance
Read the bands starting from the side where they are closer together. If the direction is still uncertain, use the tolerance band: gold and silver are never significant digits, so when you see one of them you are looking at the end of the code, not the beginning.
The E series field is a useful cross-check: if the value you decoded does not belong to any standard series, the resistor has usually been read in the wrong direction.
Combinations with all digits equal to zero do not exist as normal resistors: a 0 Ω part is a jumper resistor marked with a single black band.
Card 2 — From resistance to color bands
This is the design case: your calculation produces a value that is not commercially available. The card searches all decades of the selected E series for the nearest standard value and returns the color bands to look for.
The deviation is the first value to check. If a divider requires 3.4 kΩ and the nearest E24 value is 3.3 kΩ, the nominal error is already −2.9% before resistor tolerance is considered. With 5% resistors, the total error can approach 8%. If that margin is unacceptable, move to E96 rather than relying on a lucky component.
The value can also be written using IEC notation: 4k7, 2R2, 1M5. This notation is common on components and schematics and avoids losing a decimal point in print or reproduction.
Card 3 — Comparing E series
| Series | Nearest | Deviation | Tol. |
|---|
The E series (IEC 60063) divide each decade into \(n\) steps in a geometric progression. The k-th value is
$$ E_n(k) \simeq 10^{k/n}, \qquad k=0,\ldots,n-1 $$The relative step between consecutive values is therefore approximately constant and is roughly twice the series tolerance. This makes the tolerance ranges of adjacent values meet without large gaps or excessive overlap. E24 at 5% has about a 10% step, while E96 at 1% has about a 2.4% step.
This card shows where the same requested value falls in each E series. It helps decide whether a closer standard value is worthwhile: moving from E24 to E96 can be simpler than combining two resistors in series.
E48 and E96 require five bands: values such as 1.13 kΩ cannot be represented with only two significant digits.
Reference tables
| Color | Digit | Multiplier | Tolerance | Temp. coeff. |
|---|
| Series | Values/decade | Tolerance | Step |
|---|---|---|---|
| E6 | 6 | ±20% | ≈ 47% |
| E12 | 12 | ±10% | ≈ 21% |
| E24 | 24 | ±5% | ≈ 10% |
| E48 | 48 | ±2% | ≈ 4.8% |
| E96 | 96 | ±1% | ≈ 2.4% |