Resistor Color Codes And Basic OHM's Law

Basic outline of how to read resistor color codes and an introduction to Ohm's Law.

Believe it or not committing resistor color codes to memory is probably one of the most difficult tasks in the field of electronics. Mainly because it is one of the first things that you have to do when you are first starting to experiment in electronics. There are many sayings out there that are supposed to help you remember the color code. In my experience I never used any of them. I just used the brute force read it until you can't forget it approach. Right off the bat we will say the basic resistor color code is Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey White. With tolerance bands being, no band, gold or silver. Let's explain the primary colors first. Each color represents a number.











Now with that knowledge here's how the resistor color code works. Say you look at a resistor, starting at the end where the colored bands are closest to the edge of the resistor, and the bands are red, red, red. (Standard resistors will always have at least 3 bands, possibly 4.) The value of this red, red, red resistor would be 2200 ohms or 2.2kohms. Now, how did I come up with that value, it's very simple actually. You convert the first two bands to their equivalent numbers, in this case 2 and 2 because the first two bands are red, the number for red is 2 so you get 22, the third band equates into the multiplier, which in this case is also 2. The formula for multiplier is 10^number. Or in this case 10*10, so if you actually wanted to formulate it you would get 22*(10^2). In the case of single resistors though formulating is a null point because it is much easier just to say ok red, red, red = 22with two zeros = 2200. Here are a few more examples to help, its really not that hard.

Blue, red, yellow 624 62 and four zero's on the end 620000 620kOhms

Orange, blue, brown 361 36 and one zero on the end 360 360Ohms

Red, orange, orange 233 23 and three zeros on the end 23000 23kOhms

Violet, Grey, Yellow 784 78 and four zeros on the end 780000 780kOhms

Pretty much that's about it. There are some other types of resistors that we will not cover here; a few of these are house-branded resistors and some mil-spec resistors, which use totally different numbering schemes. You will not see these types of resistors very much so we will not go into it here.

Now on to the fourth band. Some resistors will have a fourth band, silver or gold. This fourth band is the tolerance band. Tolerance in resistors is defined, as how much the value of the resistor can be off from the stated value and still be considered useable.

No fourth band on the resistor is a 20% tolerance.

Silver fourth band on the resistor is a 10% tolerance.

Gold fourth Band on the resistor is a 5% tolerance.

If you have a red, red, red, gold resistor you have a 2200Ohm or 2.2kOhm resistor. With the gold band the resistor can be between 2090Ohms and 2310Ohms or 2.09kOhms and 2.31kOhms and still be considered good. If the fourth band were sliver the measured value could be between 1980Ohms and 2420Ohms. You just take the percentage value and figure it into the resistor value the formula looks like this: R+(R*Rt) for upper value and R-(R*Rt) Rt=Resistor Tolerance Value R=Resistor Value. The example in this case would give you 2200+(2200*5%)=Tolerance upper value 2200-(2200*5%)=Tolerance Lower Value. If the measured resistor value falls above or below these formulated numbers then the resistor is bad and should be replaced or not used. For the other values just plug in the percentage equivalent to the color of the fourth band.

Resistors are not that hard to work with, and are one of the first steps into basic electronics. Have fun with this information, and start building projects. Bring this GREAT hobby and industry of electronics back to the level that it once was.

Now on to Ohm's law. Ohms law is the basic principle of electronics stated in the formula E=I*R. One note here I am old school electronics and have always and always will be in the habit of referring to Voltage as the formula value of E. The value in some text's is referred to as V for voltage. My training of electronics used E, which stands for Electromotive force. So E= Electromotive force = V = Voltage. This note is just so my formulas do not confuse you. So in the formula E=I*R the explanation is the Voltage in the circuit MUST be equal to the Current times the Resistance. E=Voltage, I=Current, R=Resistance. The simplest way to do this is to write out the formula as:




Look at the variables, if you want to, use your finger to cover the value that you are searching for and then figure the other two. There are only 3 equations total in the formula... they are:


E/I = Resistance

E/R = Current

If you know the Voltage and the resistance and need to find current you would use formula E/R=I

If you know the Current and the Resistance and need to find voltage you would use formula I*R=E

If you know the Voltage and the Current and need to find resistance you would use formula E/I = R.

This is the basic breakdown of Ohm's law. Ohm's law does get a little more in-depth, but these are just the basics. Hope this helped you. Have fun with electronics!

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