TUTORIAL | ELECTRONICS
Understanding Resistors and Reading Resistor Color Codes
Learn the essentials of resistors, from understanding their role in circuits to reading color codes like a true engineer.
Introduction
Hey all! In this article we’ll cover what resistors are, how they function, and what their role in electronics is.
We’ll also learn how to read resistor color codes, which are colored bands placed on the body of the resistor in order to mark its value.
Resistors: Their Purpose and Importance in Electronics
A resistor is an electronic component.
When a current is sent through a resistor, it creates a voltage drop, thus reducing the source voltage.
They are essential in electronics, as they allow for high voltages to be turned down just enough so that circuits can remain in their happy, non-fried state.
One common usage for them is stepping down the voltage of a 9V (9 volt) battery into a more manageable 3.3V or 5V, which is useful when prototyping circuits on hardboards and breadboards, and when learning electronics.
Quick Note
It is important to remember that resistors are never polarized, which means that you can send a current through either one of the resistor’s legs and it will still work the same way.
What is Resistance and What’s Its Role?
Resistance, as the name suggests, represents the work that current must do when passing through a circuit.
Think of it as the force acting in the opposing direction of the current, which the current must overcome, thus slowing it down.
Any component has an internal resistance, even the wiring that goes into circuits.
Resistors are components that are specifically designed to have a resistance, usually higher than the internal resistance of other components.
Resistance plays a crucial role in electronic circuitry. It protects components from high voltage and manages current by limiting the voltage.
Quick Note
Remember that resistance is measured in ohms, denoted with the uppercase Greek letter ‘omega’, or ‘Ω’.
So, you can say that a resistor has a value of five hundred ohms or write it down as 500Ω.
The ohm is a unit in the International System of Units — The Metric System™️ — and thus there are other ways to condense it into less syllables. For example, 1kΩ is 1 kiloohm, which is 1000Ω.
Different Types of Resistors
There are many different types of resistors, some of which are:
- The basic resistor: this is the most common type of resistor. It has a set resistance value that doesn’t change. Useful for limiting the voltage going to a component so that it doesn’t fry;
- The photoresistor: this resistor’s resistance value changes based on the light reaching it. For example, if the photoresistor has a normal resistance of 500Ω when dark, when it gets hit by light the resistance will decrease 5Ω (Not representative to the actual units, but the same mechanism would apply). Useful for detecting light by, for example, only allowing current to flow once enough light hits it;
- The thermistor: this resistor’s resistance value changes based on its temperature. Useful for detecting heat by only allowing current to pass when the thermistor’s resistance is low, indicating high heat;
- The potentiometer: this is a special resistor. It has a knob that can be turned to manually alter the resistance by prolonging the distance travelled by the current through the resistive material. Useful for manually changing the value going to a component, which can change its behavior. For example, turning the volume of a speaker up or down by decreasing or increasing the potentiometer’s resistance.
These are just some examples that I could think of now, but there are others too.
The Origin and Purpose of Resistor Color Codes
The color codes for resistors, which are represented by either 4 or 5 different bands on the body of the resistor, were invented out of necessity.
Before them, electronics engineers had to test each resistor’s value with a multimeter to determine if they were the correct one to use.
By simply having some colors on the resistor, an engineer simply had to memorize what each color represented, after which, they could tell at a glance what resistance each resistor had.
It was decided that color bands would be more practical, as most resistors are pretty small, and it would be hard to read numbers if they were to simply write the value on the resistor.
Each color corresponds to a different number and represents values like digits, the multiplier, and the tolerance.
How to Read Resistor Color Codes, a Step-by-Step Guide
There is a certain order that the bands are in.
If the resistor has 4 bands, the first two digits represent the first and second digits of the resistor’s value, in order.
If the resistor has 5 bands, the first three digits represent the first, second and third digits of the resistor’s value, in order.
Then after the first either 2 or 3 digits, depending on the number of bands, comes the multiplier.
The multiplier is the power of 10 by which you multiply the number formed by the first 2 or 3 digits to get the actual value of the resistor in ohms.
The last band can have 2 colors: gold or silver. This band represents the tolerance, which is the acceptable margin of error for the value. If it is silver, the tolerance is 10%, and if it is gold, the tolerance is 5%.
I normally try to identify the last band first and then count from the opposing end.
I would also say that normally the real margin of error encountered is negligible, and for most applications, like breadboard testing, you shouldn’t worry about the tolerance, unless of course, you need a very precise value — or are working with very high values, in which case even a 5% difference can be immense.
Time For Some Examples!
Let’s take some common values and convert them into their color codes.
Also, most resistors use only 4 bands, not 5, and here I’ll be writing down just the first 3 digits, as again, I don’t really care about the tolerance.
For a 100Ω resistor, the first 3 colors will be Brown-Black-Brown
For a 220Ω resistor, they will be Red-Red-Brown
For a 330Ω resistor, Orange-Orange-Brown
For a 470Ω resistor, Yellow-Violet-Brown
For a 1kΩ (1 kiloohm) resistor, Brown-Black-Red
For a 10kΩ resistor, Brown-Black-Orange
For a 100kΩ resistor, Brown-Black-Yellow
For a 1MΩ (1 megaohm) resistor, Brown-Black-Green
These are some standard values. You can find any other value; they are just less common.
In my opinion, if you are in need of a specific value but are in the middle of two of these standard values, you should go for the higher value.
Sure, the buzzer might not buzz as loudly or the LED might not run as brightly, but it’s better to prioritize the component’s lifespan, which gets dramatically reduced if it expects a certain resistance and you give it a smaller one.
In some cases, the component might not run, as there isn’t enough current flowing through to allow it to go, but that’s all there is to risk. A higher resistance value cannot harm your components, it will simply prevent them from running, while a lower resistance can very much damage the components.
It is common to have to step down from 9V to 5V for something like an IC or 3.3V for something like an LED.
285Ω will step you down to 3.3V. The closest standard values are 270Ω, and 330Ω, so it will be Red-Violet-Brown or Orange-Orange-Brown respectively.
200Ω will step you down to 5V. It will be Red-Black-Brown
Here’s a Tip for You
We can calculate the resistance value we need for a circuit by taking the desired voltage drop and running it through Ohm’s Law alongside the current.
So again, Ohm’s Law here would be R = ( Vdrop / I )
Here, Vdrop is the voltage drop (calculated by taking the difference between the input and desired output voltage) measured in volts, I is the current measured in amps/amperes, and R is the resistance value measured in ohms.
For example, for stepping down from 9V to 5V, say to input into an integrated circuit, the voltage drop is 4V (9V — 5V = 4V). And assuming that you’re using a normal 9V battery as a source, the current would be about 20 milliamps, or 0.02A. So, R = 4V / 0.02A = 200Ω.
How to correctly read the bands
As I stated before, I prefer first identifying the tolerance band and then going from the other end. This way, I can rule out that band and start decoding the other bands in my mind.
I want to make some suggestions before letting you go from this section.
Remember that a lot of colors look similar when they are in a small place, especially given that a lot of resistors have an off-white backdrop color that kind of blends certain colors together. It is common to confuse red and brown, or on the tolerance band, confuse silver and gold — trust me, I have to wear glasses, and those colors drive me insane.
I very much recommend that you work in an evenly lit environment that’s as bright as you can take. This will make it easier to differentiate between the colors.
If your lightbulb decided to break, you can always just hold a flashlight to it. And also, be prepared to get that resistor 4 inches from your eyeball, especially if you also wear glasses, as no light in the world can make you actually see the colors from ‘too far’.
If you still can’t tell the colors apart, I recommend a small magnifying glass — I have a small one attached to an emergency whistle and it works perfectly fine — but I would discourage using your phone’s camera to digitally enhance the image, as the auto-focus often makes it even harder to see what you are looking at.
Color Code Reference Sheet
Courtesy of: AllAboutCircuits.com
I arranged them in the order of 1. bands that denote the digits, 2. that denote the multiplier, and finally 3. that denote the tolerance. If a number is missing, then it means that color doesn’t represent either a digit or a tolerance.
- Black: 0, 10⁰ (Or just 1Ω);
- Brown: 1, 10¹ (10Ω), 1%;
- Red: 2, 10² (100Ω), 2%;
- Orange: 3, 10³ (1,000Ω / 1kΩ);
- Yellow: 4, 10⁴ (10,000Ω / 10kΩ);
- Green: 5, 10⁵ (100,000Ω / 100kΩ), 0.5%;
- Blue: 6, 10⁶ (1,000,000Ω / 1MΩ), 0.25%;
- Violet: 7, 10⁷ (10,000,000Ω / 10MΩ), 0.1%;
- Gray: 8, 10⁸ (100,000,000Ω / 100MΩ);
- White: 9, 10⁹ (1,000,000,000Ω / 1GΩ / 1 gigaohm)
Gold and Silver don’t represent a digit, but they do represent a multiplier:
- Gold: 10^-1 (0.1Ω), 5%;
- Silver: 10^-2 (0.01Ω), 10%.
If there is no tolerance band, then the tolerance is +/-20%.
To illustrate tolerance: if you have a resistor advertised for 1000Ω with a tolerance of 20%, then the actual value could be anywhere from 800Ω to 1200Ω. If that same resistor had a tolerance of 10%, then the actual value could be anywhere from 900Ω to 1100Ω, and so on.
Practical Applications and Why Resistor Values Matter
Understanding resistor values is very important in applications such as dimming LEDs or controlling a motor’s speed. Resistors protect components from high voltage, so they are often placed before sensitive components like integrated circuits, buzzers and other bigger parts.
They are often used in their potentiometer form to increase or decrease the current that goes to a circuit so that, for example, a radio can change its volume.
Closing Thoughts
I hope that this tutorial has helped you learn more about resistance and how to identify different resistors by their color codes.
Also, I didn’t have where to mention this but know that resistors work whether they’re controlling direct current or alternating current.
I encourage you to go practice so that it really sticks.
After you’re done learning about resistance, perhaps you would like to learn about the difference between parallel and series circuits. I also plan on making a tutorial on that in the near future, so stay tuned!
If you enjoyed my explanation, please consider commenting on what you would like me covering next or share your own projects.
And don’t forget, practice makes perfect!
Further Reading
Some AI assistance was used to streamline the structure and clarify technical language.
