Inductors code calculation.

Inductors produces magnetic field when current passes through them. They store current in form of magnetic field unlike a capacitor which stores current in form of static charges on it plates.  The magnetic field produces current which opposes any changes in current or voltage value. As usual, it is necessary to learn how to calculate a long lead inductor's inductance for you to choose the correct inductor for your circuit and ease to buy from a retail shop, because not all shop keeper can calculate their inductance value for you he will just give you anyone in radom  for him to generate sells 😆, so you are advised to learn it by heart and understand it, so let's go! Long leads or through hole inductor's inductance value is usually calculated by their color codes just as how resistors are calculated. Big inductors have their value printed directly on them because they are big to take the numbers while small ones are printed with color codes. Here are the ways or systems inductance are calculated.

1. Inductors value using text marking.

Big resistors have their inductance value written on it which contains numbers and alphabets. It consists of four figures, the first two numbers are significant while

the third is the multiplier. It has a last figure which is an alphabet, this indicates the tolerance value. Here are common alphabets and their values.

For example a code of 255F  printed on an inductor inductance value can be calculated as follows; The first two digits is significant(written side to side) which is 25, the third number is the multiplier (multiplication of ten in number of place of 5 i.e ten is multiplied five times.)  It results to 25×10^5= 2500000.  The last alphabet  (F) is decoded as shown in the table above + or - 1%.  Therefore the inductance of the inductor is 2500000uH. Note: the Inductance unit must be in micro Henry (H) if calculated using the system above.

2. Four bands color Inductor code  system.

In this system the color codes are four just like that of resistors. It is use for smaller size Inductors for calculating thier Inductance. The first two color codes are significant while the third is the multiplier, the fourth color code represents the tolerance value. The Inductance value is usually calculated by starting with the color band nearest to the edge of the Inductor. The nine colors use for calculating  are shown below with their values. When the below color strips are used as the 1st Band or 2nd band of inductors below are their codes. 

Black............................0 Brown..........................1 Red...............................2 Orange.........................3 Yellow..........................4 Green...........................5 Blue..............................6 Violet............................7 Grey..............................8 White...........................9 

When color codes are at the 3rd band they're use as multiplier, below are colors which can fall at the band placement and their multiplier values. 

Silver..........................0.001 Gold.................................0.1 Black............................10^0 Brown..........................10^1 Red...............................10^2 Orange.........................10^3 Yellow..........................10^4 Green...........................10^5 Blue..............................10^6 Violet............................10^7 Grey..............................10^8 White............................10^9 

Below are also the colors use for inductor's tolerance value and their code values.   

Gold............................+or-5% Silver..........................+or-10% Black...........................+or-20%

Examples: 

1. Calculate the Inductance of the Inductor below.

Solutions.

The inductor above is a four band type, to calculate it inductance value we have to apply the color code number equivalents. 

The first band is the one nearest to the end, and that is brown, the second band is black followed by Gold and white. 

1st band= brown= 1 2nd band=black=0 3rd band=Gold which is a multiplier of 0.1 4th band= white which is the tolerance value. So to calculate the inductance we write as follows; 

First band value followed by second band, third band and fourth band. Thus inductance= 1,0,0.1,+or-? =10×0.1 =1uH. 

Note: 

The last which is white and usually use to calculate the tolerance value. White don't have a tolerance value and therefore it value is considered as null. Also the final inductance value must be in micro (u) farad.

3. Five bands color Inductor codes system.

Here some inductors have five  bands printed on them.  The first band which is the thickest is known as the  military radio frequency indicator and is always silver, the next three color codes are the significant figures followed  by the last which is the tolerance. The total inductance is usually micro henries (uH). Below are the color and codes values for five band inductors.

For inductors which have an inductance value less than 10uf, if gold is made the second or third band it's value is  written as decimal. 

For example a five band inductor with a value of silver(Military band), red-2, gold(.), yellow-4 & black-(+or-20%). It's value is calculated as 2.4uf. Also if the second band is gold, for example Silver, gold, red, yellow, black. The gold value will be 0. Therefore inductance = 0.24uf.

Note: To calculate the inductance value of a five band inductor, the first band is usually white, so the value should be calculated starting from the second band after white.