This post is going to be another short one that covers some basics but may also be a good review for electronics veterans alike.
The topic is resistor color code.
If you’re just starting in electronics you don’t want to miss this one as it will discuss one of the most basic yet important things you need to know.
Now, I know some of you may be thinking something like “…yeah, but there are resistor color code calculators online so why bother?”
Right, there are some helpful resistor color code calculators out there that can help you when you’re learning. Use these to check yourself in the beginning.
But it would be a lot more efficient and quicker if you could know the value of a resistor within a second or two just by looking at it.
Oddly enough, none of the courses I had to take to get my degree in electrical engineering talked about this. Nor do I recall any of the texts mentioning it.
Previous to college and my EE degree, I earned a diploma in electronics, computers, and robotic technology at a for-profit tech school. This took me one year.
There, resistor color code was one of the first things we learned.
By the way, if you want to know more about resistors, here is a post about resistor types and their differences.
Now on to color code…
Intro to Resistor Color Code
As the electronics industry evolved, one of the first things that the industry’s players did was standardize the color code marking on resistors. Resistor manufacturers adopted this color code.
The first band you start with when reading resistor color code will be closer to one end of the resistor.
In the figure below, we see that the brown band on the left is the one closest to one end of the resistor and therefore the one we start with when determining its value.
Figure 1: the brown band is the one we start with because it is closer to one end of the resistor
Although resistors with four bands (like the one in the picture above) are the most common you’re likely to run into as a hobbyist, there are resistors that use a five band and even a six-band color code.
We’ll talk a bit more about why in a minute.
But first, let’s have a look at the helpful chart below, which came from a text book of mine. I had to edit the figure because for some reason they did not include the multiplier value for grey and white. Though it’s unlikely you’ll be working with resistors in the gigaohm range very often, they do exist.
Referring to this diagram as you read will make understanding resistor color code a breeze.
Figure 2: resistor color code chart
The left column of the chart starts with a helpful mnemonic for remembering the colors and their order. There are other mnemonics for this which we’ll touch on later.
The third column assigns a number to each color.
The fourth assigns a multiplier to each color. Notice that the number of zeroes is equal to the color’s number. For example, the color orange represents the number 3 and a multiplier of 1000, which has 3 zeros.
On top of the chart, we can see a picture of a normal four-band general purpose resistor and a five-band precision resistor. This graphic tells us what each of the numbers from the chart means.
On a four-band resistor we can see that the first two bands represent the first two digits of the resistor’s value. The third band is a multiplier, which tells us what to multiply the first two digits by to get the ohmic value of the resistor. Finally, the fourth band gives us the tolerance of the resistor, which is just a way to measure the variation of real ohmic value between different batches of resistors.
For example, if the first 3 bands were red and the fourth was gold, we’d have a 2,200-ohm resistor with a 5% tolerance. The first two red bands give us the first two digits, which are 2 and 2. The third red band tells us to multiply this by 100 (notice the two zeros in 100). The fourth band gives the tolerance. Because this is not a precision resistor, the chances of it being exactly 2.2k ohms is extremely small.
Rather, because of the 5% tolerance we can expect any given resistor with these markings to measure somewhere between 2,090 ohms and 2,310 ohms if we put an ohmmeter across it.
For many applications, this may be acceptable. If we needed a tighter tolerance, we could switch to a five-band precision resistor.
For example, if we had a five-band resistor whose colors were red, red, red, red, and violet we’d have a 22,200-ohm resistor with a 0.1% tolerance. This is likely the best you’ll see as far as tolerances go. We get this value because red represents the number 2. Only this time, since it’s a five-band resistor, the first 3 digits are 2s and the fourth red band represents the multiplier of 100. The fifth band is the tolerance.
If we put our ohmmeter across this resistor we can expect the value to be between 22,177.8 ohms and 22,222.2 ohms. As we can see, this is pretty darn close to the expected value.
Note that you will never see a resistor that starts with a black band as black is the color for zero. The only exception to this is the zero-ohm resistor which has only one black band and no others.
Resistor Color Code Practice
Let’s try a few practice problems to hone our skills at deciphering resistor color code. The answers are given at the end of the post. No peeking!
Ex. 1: A four-band resistor has the colors (starting with band one): green, blue, brown, gold. What is its resistance and tolerance?
Ex. 2: A five-band resistor has the colors (starting with band one): red, red, green, gold, brown. What is its resistance and tolerance?
Ex. 3: A four-band resistor has the colors (starting with band one): gray, black, black, no fourth band. What is its resistance and tolerance?
Resistor Color Code Mnemonics
From the chart in figure 2 we already know one mnemonic or memory aid for color code. That one goes:
Big (for black) Beautiful (brown) Roses (red) Occupy (orange) Your (yellow) Garden (green) But (blue) Violets (violet or purple) Grow (gray) Wild (white) So (silver) GetSome (gold).
There are two other mnemonics for remembering color code.
One of them may be offensive to some people.
If you’re easily offended, don’t read it. If you do read it and get offended please don’t leave nasty comments or be mad at me. You were warned. I did not come up with it, and, in fact, this is the mnemonic taught in my tech school, with classes consisting of both men and women. I doubt the people who attend this school are the only ones who’ve heard of it, as I’ve seen it referenced before.
The potentially offensive version goes: Bad Boys Rape Our Young Girls But Violet Gives Willingly So GetSome.
The less offensive version of this one is somewhat similar and goes: Boys Race Our Young Girls But Violet Generally Wins.
Of course, adding So GetSome to the end of this wouldn’t make sense so you’ll just have to remember that silver and gold come after the color white.
6-Band Resistor Color Code
Believe it or not, there are resistors with 6 bands. The average hobbyist probably won’t see these very often (or at all), but they do exist.
To read a six-band resistor, we treat it just like a 5-band resistor with the 6th band representing a temperature coefficient.
This band indicates how much the actual resistance value of the resistor changes when the temperature changes.
The picture below is a color code chart for 6-band resistors. I’m not going to go into detail about the temperature coefficient in this post, but the chart can help if you run into one of these.
Figure 3: 6-band resistor color code
The Zero-Ohms Resistor
You now know that zero-ohm resistors exist. These resistors have one black band on them to represent zero ohms. There are no other bands.
But why bother making a zero-ohm resistor?
A zero-ohm resistor is equivalent to a straight piece of wire or a jumper wire.
Many PCBs are assembled and soldered by machines, not humans. Since the equipment used to assemble PCBs handles resistors and not wires, the zero-ohm resistor is used in place of where there’d normally be jumper wires.
That’s the purpose of zero-ohm resistors.
Answers to Example Problems Above
Ex 1: The colors on the four-band resistor are: green, blue, brown, gold.
Remembering our mnemonic of choice, we know that green represents the number 5, blue represents 6, and brown tells us to use a multiplier of 10 (notice 10 has one zero and brown represents the number one). Because it’s a four-band resistor, the first two bands represent the first two digits.
So, we have: 56 * 10 = 560 ohms. The gold band tells us this resistor has a 5% tolerance.
Ex 2: The colors on the five-band resistor are: red, red, green, gold, brown.
Once again, we delve into our memory and access the mnemonic of choice. We remember that red represents the number 2 (there are 2 twos), and green the number 5. Remember that on a five-band resistor the first three bands represent the first three digits. In this case, the gold band is the multiplier. This is due to the fact that the fourth band on a five-band resistor is the multiplier. It is 0.1 in this case.
So, we have: 225 * 0.1 = 22.5 ohms. The brown band tells us this resistor has a tolerance of 1%.
Ex 3: The colors on the four-band resistor are: gray, black, black, none (you’ll just have to imagine the fourth band is there).
We know that gray represents the number 8 and that black represents zero (there are 2 of them).
So, we have: 80 * 1 = 80 ohms. Remember, when a black band is in the multiplier position it simply means to use a multiplier of one (with no zeros).
The absence of a fourth band indicates that its tolerance is 20%.
Bonus Question: If you were measure each one of these with your ohmmeter, what are the low and high values you’d expect from each resistor?
You Can’t Resist Resistor Color Code
Thus concludes our post on resistor color code. Remember, there are plenty of online calculators to check your work when you’re first learning color code. With a bit of practice, you’ll be able to gaze at a resistor and rattle off its value in a matter of seconds.
In the future, I may add my own color code calculator to this site.
Until then, comment and share your (offensive or non-offensive) mnemonics you use for color code.