How to Calculate 3 Band Resistor Color Code? A Step-By-Step Guide

Resistor color codes are an important tool used by electrical engineers to quickly and accurately determine the resistance of a resistor. Knowing the resistor value is essential for designing electronic circuits, so understanding how to calculate resistor color codes is an essential skill. This guide covers the basics of calculating 3-band resistor color codes, providing a step-by-step process for making your calculations quickly and accurately.

The importance of resistor color codes can not be understated. By using these codes, engineers can easily compare different resistors without having to manually measure them with a multimeter or calculator. Not only does this save time and effort, it also ensures that the circuit design is accurate and reliable.

This guide will provide an overview of how to calculate 3 band resistor color codes and provide a step-by-step process for doing so. Specifically, this guide will cover:

  1. How to identify the colors on a three-band resistor
  2. How to read the values on a three-band resistor
  3. What type of number notation should be used when calculating 3-band resistors?
  4. How to calculate 3 band resistors using OHM’s Law

Understanding the 3-Band Resistor Color Code

A three-band resistor color code is a way of identifying different resistor values. It is a standardized set of colors that represent specific numbers and multipliers, making it easy to determine the resistance value of a resistor quickly and accurately.

The chart below shows the various colors used in three-band resistor color codes and their corresponding values:


Each color represents one or two digits, while the multipliers will adjust the number to get the total resistance reading. For example, a resistor labeled with brown, black, and red would be written as “10 x 100 = 1 kΩ”, meaning it has a resistance of 1000 ohms plus or minus 20%. The tolerance color indicates how accurate the reading is likely to be (in this case 20%).

Finally, the significance of each color band should not be overlooked. Every digit and multiplier in a resistor color code has its own purpose, so understanding what each one means is essential for calculating your resistor values correctly.

How to Calculate 3 Band Resistor Color Code?

You can Calculate your resistor value within a few seconds using our Resistor Color Code Calculator.

Calculating a 3-band resistor color code is relatively simple and straightforward. To calculate the resistance value, you need to use the formula R = (first two colors) x (third color):

R = (1st Color x 10) + (2nd Color) x (3rd Color)

For example, if you have a resistor labeled brown, black, and red, it would read as 1×10+0x100 which equals 1000 ohms (1kΩ).

Now let’s look at how to calculate 3 band resistors with a step-by-step guide:

  1. Identify the colors on your resistor. The first two colors represent digits and the third color represents a multiplier.
  2. Determine the first two colors’ numerical values according to the chart above. For example, if the resistor has brown and black bands it can be written as 1×10+0.
  3. Determine the third color’s numerical value by referring to our color chart above. If it’s red, then it can be written as 100.
  4. Calculate your total resistance by multiplying your first two numbers by your third number: 1×10+0x100=1000 ohms (1kΩ). When done correctly, this should give you an accurate reading of what your resistor is measuring in ohms.
  5. Finally, remember to check the tolerance value of your resistor to ensure accuracy. This is usually indicated by a 4th colored band on the end of most resistors; for example, if it’s silver then it has a ±10% tolerance rating.

Practice makes perfect! Try calculating some 3-band resistant values with these practice exercises:

  • Brown Black Red =? Answer: 1000 ohms (1kΩ)
  • Red Orange Gold =? Answer: 27000 ohms (27kΩ)

Determining the Tolerance Rating

The tolerance rating is an important indicator of the accuracy of a resistor. It tells you how much the resistance could vary from its stated value and can range anywhere from +/- 0.01% to as high as 20%. Knowing this number will help you gauge your calculations more accurately.

To determine the tolerance rating, look for the fourth color band on the end of most resistors. This will provide you with an indication as to how accurate your readings are likely to be when measuring the resistance value:

Brown±1%, ±2%, or ±5%
Green±0.5%, or ±0.25%

For example, if your resistor has a silver-colored band then it’s got a 10% tolerance rating; meaning its actual resistance reading could be up to 10 percent different than its stated value.

Let’s try some practice exercises to solidify our understanding of determining tolerance ratings:

  • Silver =? Answer: ±10%
  • Brown =? Answer:±1%, 2

Checking for the Temperature Coefficient

The temperature coefficient of a resistor is an important consideration when measuring resistance values as it accounts for any changes in resistance that may occur due to temperature variations. Most resistors have a temperature coefficient rating of either 25ppm/°C (positive) or 30ppm/°C (negative). To determine if your resistor has a temperature coefficient, look for the fifth color band on the end. If its present, then your resistor is likely to have a temperature coefficient value:

ColorTemperature Coefficient

For example, if your resistor has an orange-colored band then it’s got a +25ppm/°C temperature coefficient; meaning its actual resistance reading could increase by up to 25 parts per million per degree Celsius.

Let’s practice some exercises to further solidify our understanding of temperature coefficients:

  • Orange =? Answer: +25ppm/°C
  • Blue =? Answer: -30ppm/°C


This guide has served as an introduction to resistor color codes and their importance when measuring resistance values. We discussed the importance of the first three color bands in obtaining the correct ohm rating, as well as how to identify the tolerance rating from its fourth band, and temperature coefficient from its fifth band.

To recap, be sure to always check for accuracy before making any calculations. Additionally, use reference charts to cross-check your results for accuracy. Lastly, if you need more assistance in learning about resistor color codes then there are plenty of online resources available for further exploration.

We hope this guide proves useful in your journey of mastering electronic circuitry!

Additional Resources

Here are some additional resources you may find useful when exploring resistor color codes:


What is the color coding of a 3-band resistor?

A 3-band resistor typically includes three colored bands that correspond to the first three digits in its 4-digit numerical value. The first and second bands represent the first two numbers, while the third band indicates the power of 10 for a multiplier digit. For example, a resistor with yellow-violet-brown bands has a resistance value of 47 x 10^1 ohms (470 ohms).

How do you calculate resistor color coding?

The most common way to calculate resistor color coding is by using an online calculator or reference chart. When using a calculator, you will need to enter the three colored bands in order and it will compute the corresponding 4-digit numerical value. You can also use reference charts that map out different combinations of colors to their respective values.

How are colour bands calculated?

Color bands are calculated by mapping out each individual color’s assigned value and then combining them according to their position on the resistor. The first band is assigned as the first significant figure, followed by the second band assigned as the second significant figure. The third band then represents a multiplier between 0 and 1000 that is multiplied to produce its final ohm rating.

How do you calculate resistor bands?

Calculating resistor bands can be done with either an online calculator or a reference chart that maps out different combinations of colors to their respective values. To use an online calculator, you will need to enter the three colored bands in order and it will compute the corresponding 4-digit numerical value for you. Alternatively, you can use a reference chart which will provide you with all of your possible combinations as well as their calculated values.

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