Resistors are measured in ohms (the symbol is Ω). The more a resistor is able to resist electrical current, the higher it’s ohm value. As they are small, a system of colored bands marked are marked onto every resistor to help people identify it’s value without having to test it. A typical 0.5 watt resistor, commonly used for small electronic prototyping, has four color bands. The first two colors represent the first two digits of the value, the third value is the multiplier, and the fourth value is the tolerance, or how much the actual resistance varies from the specified resistance. Usually the tolerance is ± 5%, so a 1000Ω resistor could have an actual value between 950 and 1050Ω.
|Color||First Digit (1st Band)||Second Digit (2nd Band)||Multiplier (3rd Band)||Tolerance (4th Band)|
To find the colors for a specific value:
- Identify the value you want. Let’s say you want a 470Ω resistor.
- Find the first color band based off of the first digit. The first digit of a 470Ω value is the 4. Looking at the chart under the first color band, the value of 4 is represented by yellow.
- The second digit is 7. Again looking at the chart for the second digit, the next band is violet.
- The third value is multiplier. You multiply the first to band values together (47) by this one to get the final value. In this case 47 * 10 = 470, so looking at the chart, the third band is brown.
- The fourth value is the tolerance. With most resistors, used by hobbyists, this value is ±5% or ±10%, gold or silver.
- So the final color banding for a 470 Ω resistor with a ±5% tolerance is yellow-violet-brown-gold.
To find the resistor value based off of the color bands :
- Using the chart look at the first two colors and match them up to the first and second digits. For example, say you had a resistor with colors red-red-brown-gold. This would mean that the first two digits are 2 and 2.
- For the third band, find the equivalent multiplier amount and multiply that by the first two digits. Since brown is representative of 10, I multiply the first two digits, 22, by 10 to get a value of 220Ω.
- The final band shows the tolerance. Referring to the chart for the value, the gold tolerance band means that the 220Ω resistor has a tolerance of ±5%.