Reading Surface Mount Resistor Codes


Introduction: 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.


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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    20 Discussions

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

    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

    2 replies

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

    You should be able to find what you need here-

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

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


    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.

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

    That is a 100% clear explanation!

    Simple but effective.


    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.


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

    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.


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

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

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

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

    Hope this helps.

    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:

    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 ...

    2 replies

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

    Should I be? When I strip boards with SMD on them I just let those parts float on the top of my solder pot until I skim it. So when I say SMT stinks I mean it literally!

    !!! "Perfect" !!!

    Exactly what ive been wanting to know to get into SMD soldering !!

    Thanks a bunch for taking the time to make this nice and simple 'ible so a complete beginner (started this year!) in electronics can easily digest !

    Keep up the GREAT work and hopefully some more write-ups on SMD's !

    Oh by the way, how would i measure the capacitance of a SMD capacitor using a DMM ??
    many thanks in advance fo a noob question but my friend google hasnt turned up much, or maybe im not searching for the right thing here, lol !!!