Reading Surface Mount Resistor Codes

About: I am work in a high voltage laboratory, the largest laboratory owned by a university. I am in love with electricity. I have been fortunate enough to work with a variety of green technology including fuel cel...

Unlike Through hole resisors which use colored bands to determine the value, surface mount resistor have numbers and sometimes letters. I will teach you how to take those letters and digits and determine the value.

Looking at the image you see 4 resistors, the first being 391  the seconed 270 and the two at the bottom are the same 30R9. That does not stand for a 391 ohm , 270 ohm, and so on. The formula for breaking the code down is as follows.
1st value-2nd value-multiplier
3              9               1             = 390 ohm resistor
2               7               0            =  27 ohm resistor
2               3               3            =   23000 ohm or 23K ohm resistor

There are some resistors which have 4 digits. The formula is the same with the addition to a digit.
1st value-2nd value-third value-multiplier
2              3                5                 3 =       235K ohm resistor

You may ask"why some have three diigits and some have four?" three digits typically means that the resistor is 5%  tolerance the four digit typically means the resistor is 1% tolerance. If a letter is used to represent tolerance use the chart below.

B=.1%
C=.25%
D=.5%
F=1%
G=2%
J=5%
K=10%
M=20%
Z=80%

Now you will notice that the last two resistor have an "R" in the equation. The way to look at these is very simple. The R represents a decimal. So 30R9 is a 30.9Ohm resistor.
R23= .23 ohm
5R6= 5.6 ohm
45R3= 45.3 ohm


 Of course you can read the values with a meter, but whats the fun in that? I hope you all learned something from this little write up.

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    22 Discussions

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    ChristianS256

    2 years ago

    I have 2EE resistor, what is the value of that? please help me... thanks a lot...

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    Shawners06

    2 years ago

    I have these capacitors out of an A/V Reciever with markings K3 47 16v. Can someone tell me the meaning and how I could purchase 10 of them. This is my first major task.Thank you for your time

    image.jpg
    2 replies
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    ColorBombShawners06

    Reply 2 years ago

    Those are SMD aluminium electrolytic capacitors, the K3 is a series number, 47uf 16V.

    You should be able to find what you need here-

    http://www.digikey.com/product-search/en/capacitors/aluminum-capacitors/131081?k=47uf%2016V%20capacitor

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    Shawners06ColorBomb

    Reply 2 years ago

    I would like to say Thank you for taking the time to Help me out. I do Appreciate

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    aadegbite

    2 years ago

    Hi, What about the underlined SMD resistor like 304 and 332. I mean ___.

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    Aman19

    2 years ago

    what would be resistor ohm value if a resistor indicate only 'D' letter and also what is for very lite colour srd resistor with out any digit.

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    DavidH303Nightshade

    Reply 2 years ago

    Maybe uUse a volt-ohm meter to determine it's resistance?

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    VinceA5

    2 years ago

    That is a 100% clear explanation!

    Simple but effective.

    Thanks

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    Lance_Tronic

    3 years ago on Introduction

    Excellent explanation of SMD Values.

    As a newbie to SMD I have found myself a little daunted by this miniature hardware, but I am now more confident of installing the correct resistor when constructing my projects.

    Lance

    - I now have a (cheap) bulk lot of mixed SMD on the way to practice my soldering skills -

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    David InnesA

    4 years ago on Introduction

    Hi Instructables, I have looked up many sites to find the best explanation on SMD resistor colour codes. Your one is excellent. I will recommend this explanation to everyone who is searching for a good basic understanding.

    Dave.

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    Can i use that usual resistor with color coding instead of SMD resistor of same value(ohms) in a project ????

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    Can i use that usual resistor with color coding instead of SMD resistor of same value(ohms) in a project ????

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    yadavneeraj

    5 years ago on Introduction

    hi,i am neeraj i m joining a new member in ur electronic world. plz.help me.

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    mstokes3

    5 years ago on Introduction

    Here's the full link. The part after and including the last % is not needed.

    http://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7F1773204%7FH%7Fpdf%7FEnglish%7FENG_DS_1773204_H.pdf

    Hope this helps.

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    mstokes3

    5 years ago on Introduction

    There is a completely different code used on some resistors. It has to do with a three number scheme that allows 1% values. I found a good reference here:

    http://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7F1773204%7FH%7Fpdf%7FEnglish%7FENG_DS_1773204_H.pdf%7F1622827-1

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    pfred2

    6 years ago on Introduction

    I like to put the surface mount resistor on a hard surface then smash it open with a rock. Then like reading tea leaves I divine what it's resistance once was ...

    1 reply
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    ColorBombpfred2

    Reply 6 years ago on Introduction

    Pfred i gather from this post ,and others, that you aren't a fan om SMD. :0)