To select the correct resistor, you need to understand resistor color codes.

Deciphering the Color Codes

Early on, the electronics industry standardized on a common color-coding system that allowed equipment designers to identify resistors and other components at a glance.

Today, the same resistor color system is still used and has been codified, most recently, by IEC Standard 60062. This IEC Standard also includes the RKM code, a system of shorthand codes to identify resistance and capacitance values on small components where decimal points may be difficult to read. At TE, we use these systems to identify some electronic components.

Our resistor data sheets use RKM shorthand codes for resistance values. The following is a brief description for those unacquainted with these codes. For resistance values without prefixes, the letter “R” is used in place of the decimal point to identify a resistance value. For example, 1R0 is shorthand for a 1.0 Ω resistor. For resistor values with only one significant figure such as 2 Ω, 2R0 is used. For kiloohm (kΩ) resistance values, a “K” replaces the decimal. Therefore, 1K5 identifies a 1.5 kΩ or 1,500 Ω resistor. Similarly, “M” represents MΩ and “G” represents GΩ. The following table provides several examples of the RKM codes for selected resistance values.

Resistor color code: resistance values

Resistor color code: resistance values

Resistors on a printed circuit board (PCB).

How to read a resistor color code. Many small resistors are marked with the IEC 60062 color code with 3-band, 4-band, 5-band, or 6-band, depending on the required precision of resistance values. To read the color code of a resistor, it is important to begin with the band closest to the end of the component. Also, the space between the multiplier and tolerance bands is slightly larger than between the digits and multiplier.

Resistor Color Code Chart: 3 & 4 Band Resistors

Resistor Color Code Chart: 3 & 4 Band Resistors

3-Band Resistors

The values of 3-band resistors have a tolerance of ±20% and are commonly used by hobbyists or when the resistance value is not critical. For a 1R0 (1 Ω) resistor with 3 bands, the colors will be brown, black and gold. The resistance value will fall between 1.2 Ω and 0.8 Ω.

Resistor Color Code: 3-Band Resistors

Resistor Color Code: 3-Band Resistors

4-Band Resistors

When tolerances lower than 20% are required, a 4-band resistor, with an additional band to specify the tolerance, is used. For a 1K5 or 1500 Ω resistor with a tolerance of ±5%, the bands will be brown, green, red and gold. In this case, the value of the resistance can vary by ±75 ohms.

Resistor Color Code: 4-Band Resistors

Resistor Color Code: 4-Band Resistors

Resistor Color Code Chart: 5 & 6 Band Resistors

Resistor Color Code Chart: 5 & 6 Band Resistors

5-Band Resistors

For more precise applications, in which additional significant figures are required, 5-band resistors allow for a 3rd digit to be specified. A 270K (270,000 Ω) resistor will have a red, violet, black and orange band that identify the value. A silver band indicates the value will fall between 243K Ω and 297K Ω.

Resistor Color Code: 5-Band Resistors

Resistor Color Code: 3-Band Resistors

6-Band Resistors

High precision resistors specify the temperature coefficient of resistance (TCR) which quantifies the influence of temperature on the resistance value when compared to 25°C (77°F). The change in resistance is measured in ppm/°C where ppm = ΔR/R or the change in resistance per Ω of rated value. A high precision resistor with a value of 68 MΩ with a tolerance of ±5% and a Temperature Coefficient of Resistance of 250 ppm/°C is depicted below.

Resistor Color Code: 6-Band Resistors

Resistor Color Code: 6-Band Resistors