Instructables
Picture of Reading Surface Mount Resistor codes
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.
Nightshade7 months ago
What if you have some without any markings at all?
yadavneeraj10 months ago
hi,i am neeraj i m joining a new member in ur electronic world. plz.help me.
mstokes31 year ago
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.
mstokes31 year ago
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
pfred22 years ago
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 ...
ColorBomb (author)  pfred22 years ago
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 !!!