The resistance color code is a way to determine the value of a resistor based on the colors of bands or dots printed on the resistor. Resistors are electrical components that resist the flow of electrical current. Each resistor has a specific resistance value, measured in ohms. The resistance color code allows you to quickly identify the value of a resistor without having to measure it with a multimeter.
How the Resistance Color Code Works
The resistance color code uses a series of colored bands or dots printed on the resistor to denote the resistor’s value. Here is how it works:
- Most resistors have 4 bands – 3 color bands to denote the value, and 1 band for the tolerance.
- The first 2 or 3 bands (depending on the resistor) denote the first two or three digits of the resistor value.
- The third band indicates the multiplier or number of zeroes to add.
- The fourth band indicates the tolerance or accuracy of the resistor value.
Each color represents a different number or multiplier:
| Color | Digit | Multiplier |
|---|---|---|
| Black | 0 | 1 |
| Brown | 1 | 10 |
| Red | 2 | 100 |
| Orange | 3 | 1,000 |
| Yellow | 4 | 10,000 |
| Green | 5 | 100,000 |
| Blue | 6 | 1,000,000 |
| Violet | 7 | 10,000,000 |
| Gray | 8 | 100,000,000 |
| White | 9 | 1,000,000,000 |
For example, a resistor with bands colored yellow, violet, red, gold would have a value of:
- Yellow = 4
- Violet = 7
- Red = multiply by 100
So the resistor value would be 4700 ohms. The gold band indicates a 5% tolerance.
4-Band Resistor Color Code
The most common resistor has 4 color bands:
- 1st and 2nd bands – Digits
- 3rd band – Multiplier
- 4th band – Tolerance
Here are the steps to read a 4-band resistor:
- Determine the values for the first and second color bands.
- Determine the multiplier value from the third color band.
- Combine the digit values and multiplier to determine the resistor value.
- The fourth band indicates the tolerance.
For example, a resistor with the following color bands:
- Brown
- Black
- Orange
- Gold
Would have these values:
- Brown – 1
- Black – 0
- Orange – multiply by 1,000
- Gold – 5% tolerance
The resistor value would be 10 x 1,000 = 10,000 ohms with a 5% tolerance.
5-Band Resistor Color Code
Some resistors have 5 bands:
- 1st, 2nd and 3rd bands – Digits
- 4th band – Multiplier
- 5th band – Tolerance
Reading a 5-band resistor involves an extra digit band:
- Determine the values for the first, second, and third color bands.
- Determine the multiplier from the fourth band.
- Combine the 3 digit values and multiplier to determine resistance.
- The fifth band indicates tolerance.
For example, a 5-band resistor with:
- Green
- Blue
- Yellow
- Red
- Gold
Has the following values:
- Green – 5
- Blue – 6
- Yellow – 4
- Red – multiply by 100
- Gold – 5% tolerance
The resistor value is 564 x 100 = 56,400 ohms with 5% tolerance.
Resistor Tolerance Bands
The tolerance band indicates the accuracy or precision of the resistor value. Common tolerance band colors include:
| Color | Tolerance |
|---|---|
| Gold | ±5% |
| Silver | ±10% |
| No band | ±20% |
For example, a 10,000 ohm resistor with a gold band has a tolerance of ±5%, meaning its actual value should be between 9,500 – 10,500 ohms. A silver band would indicate ±10% tolerance.
Resistor Tables and Charts
For quick reference, you can use resistor color code tables or calculators to determine resistance values:
- Tables – Match the color bands to the resistance value
- Calculators – Input the colors to calculate the value
- Apps – Mobile apps to decode resistor colors
Here is an example resistor color code table:
| Band 1 | Band 2 | Band 3 | Resistance Value |
|---|---|---|---|
| Red | Yellow | Orange | 2,400 Ohms |
| Brown | Green | Orange | 1,500,000 Ohms |
| Blue | Grey | Black | 68 Ohms |
These tables or calculators make it easy to quickly identify resistance values.
Variable Resistors
Variable resistors, also called potentiometers, have 3 terminals and a sliding contact that can vary the resistance. Common types include:
- Rotary potentiometer – Dial that rotates through resistances
- Slider potentiometer – Slider that adjusts resistance
- Rheostat – Adjustable resistor that can act as a variable resistor or fixed resistor
Potentiometers may have the resistor value and tolerance marked on them, but the resistance depends on the adjustment of the dial or slider. To determine the resistance, you need to measure it with a multimeter.
Specialized Resistors
There are many other specialized types of resistors beyond the standard cylindrical ones:
- Surface Mount Resistors – Tiny rectangular resistors for circuit boards
- Chip Resistors – Tiny rectangular blocks
- Wirewound Resistors – Coils of wire act as the resistor
- Foil Resistors – Resistive metallic foil
- Power Resistors – Large resistors to handle high power
These types of resistors may have unstandardized color coding or none at all. Again, a multimeter would be needed to measure the resistance.
Conclusion
The resistor color code is a simple and efficient way to identify the value of resistors without measuring them. Using the color bands, you can quickly determine the resistance and tolerance to understand the performance of a resistor. With a basic knowledge of the color code, you can easily read 4-band and 5-band through-hole resistors by matching the colors to the standard values. For variable, specialty, or surface mount resistors, you may need additional details from markings or to take multimeter readings. Whether you are a hobbyist, electrician, or engineer, familiarity with the resistor color code is essential for working with this common electrical component.
