For small Inductors like air-core, iron-core, ferrite-core or SMD inductors etc., the surface area of the component is very small hence it is not possible to print the exact value of inductance and other parameters (nameplate rating) on it. This way, some special notations and marking are used e.g. color bands, color dots, digits, numbers and alphanumeric characters which known as inductor color codes and they are used to indicates the different characteristics and values of inductance of inductors. Generally, the values of these indictors are in μH (Microhenries 1 x 10^{-6}).

Let see how to read the value of inductors by using the standard marking codes?

2 Numerical Values:

If an inductor has two numerical values, or any two digits and a letter like 11N, it means the value is 11 nH (nanohenry).

If there is a letter (mostly R which shows dot “.”) in the middle of two digits like 6R8, it shows:

For example: 6R8 = 6.8 μH.

If the first or middle letter is “μ”, “p” or “n” instead of R, it represents the main units of Inductance such as

For examples:

5μ = 5 Micro-henry

3μ1 = 3.1 Micro-henry

N42 = 42 Nano-henry

3 Numerical Values:

Most of the inductors have three numerical values printed on it. For example, 220, 221, 222, 223, 331, 332 etc. Let’s see how to read these values. Suppose the printed value on an inductor is “332”

332 = 33 x 10^{2} = 3300 μH (Microhenry)

Similarly, if the specials marking code on the inductor is 223J: (3 Digits + 1 Alphabet), the fourth one character (“J” in this case) shows the tolerance of the inductor: For example:

Apart from the text marking on inductors, there are special inductor color codes namely “EIA” (Electronic Industries Association) and “Mil-Spec” (Military Specification). There are three, four or five color bands printed on the inductor which shows the inductance of the inductor and tolerance. Let’s see how to read 2, 3 and 4 bands color codes inductor as follows:

Reading 3 bands Inductor Color Codes

If there are three color bands marked on an inductor, it means

1^{st} Color Band = First Number of Value of Inductor.

2^{nd} Color Band = Second Number of value of Inductor.

3^{3rd} Color Band = The number of Zeros (as multiplier) with the first two digits of inductor (In numbers).

Example:

The Three color bands inductor as Red, Brown & Gold:

Red = 2, Brown = 1 & Gold = 0.1 i.e.

= 21 x 0.1 = 2.1 µH

Mostly, the three color band inductors have a tolerance of ±20%. This way, the value of the inductor is 2.1 µH – ±20%.

The following table shows the three bands inductor color codes and its values.

If there are five color bands printed on an cylindrical molded inductor, it means

1^{st} Color Band = Mil-Spec (Military Specification) Identifier – Always Double-Width Silver Band / Strip which identifies the military radio-frequency inductors.

2^{nd} Color Band = First Number of Value of Inductor.

3^{3rd} Color Band = Second Number of value of Inductor.

4^{th} Color Band = The number of Zeros (as multiplier) with the first two digits of Inductor (In numbers).

5^{th} Color Band = Tolerance in percentage.

Example:

The Five color bands inductor as Silver , Red, Blue, Brown & Gold:

Silver = Mil-Spec, Red = 2, Blue = 6, Brown = 10, & Gold = ±5% i.e.

= 26 x 10 = 260 µH

The fifth band as Golden color shows the tolerance of ±5%. Therefore, the value of the inductor is 260 µH – ±5%.

The following table shows the four bands inductor color codes and its values.

Inductance Value Code to Inductor Color Codes Calculator

The following calculator will convert the value of inductance printed in code on an inductor to the four bands of inductor color codes. This calculator supports 4-colored strips and values of inductances in H (Henries), mH (milli-henries) and µH (micro-henries). Just put the code of the inductor in digits e.g. 100, 102, 233 etc and click on calculate for the desired color codes.

Enter Values

Enter Inductor Code:

H – (Henrys)mH – (MilliHenrys)µH – (Microhenrys)

Tolerance %:

5% 10% 20%

The Color Code is:

Reading Chip & SMD (Surface Mount Device) Inductor Color Codes

On SMD inductors, there is no possibility to print the inducting marking or color code bands due to the small surface area of the tiny component. This way, only colored dots are printed on these inductors to represent the value of inductance in nanohenries. Keep in mind that these dots do not represent the polarity of the inductors and can only be used in clockwise direction to determine the value of SMD inductors.

For Example:

The colored dots in clockwise direction on an SMD inductor are Yellow, Blue & Red. This way:

Yellow = 4

Blue = 6

Red = 10^{2}

Hence the value of the SMD inductor is 4600 nH.

Reading RF (Radio Frequency) Inductor Color Dots Codes

Radio frequency or RF inductors are the same like SMD and chip inductors in size. The marking method is the same as the above one i.e. if there is only one color dot, it shows the inductance and other specifications can be seen in the related datasheet.

On the other hand, if there are three colored dots printed on the RF inductors, the first two opposite colored dots (in clockwise direction) show the first and second digit (significant figures) respectively while the single dot on the other end represents the multiplier.

Good to know: The single or three dots are not supposed to represent the polarity of the inductor but only the value of inductance in nanohenries (nH).

For Example:

The colored dots in clockwise direction on an RF inductor are RED, RED & Gold. This way:

Red = 2

Red = 2

Gold = 0.1

Hence the value of the RF inductor is 2.2 nH.

The following table shows the 1008 and Midi Spring Series Inductor 3 – Color Dots Codes and its values of inductances in nH.

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