4band

4band, in the context of electronics, refers to the four-band resistor color code used to encode the resistance value of axial resistors. The code employs four colored bands arranged along the body of the resistor to convey its electrical resistance and tolerance, enabling quick identification without measuring equipment.

How it works: the first two bands represent the significant digits of the resistance value. The third band is a multiplier, indicating the power of ten by which the two digits should be scaled. The fourth band indicates tolerance, describing how precisely the resistor’s value is within specification. A common example is brown, black, red, gold, which decodes as 10 × 100 = 1000 ohms (1 kΩ) with a ±5% tolerance.

Color mapping and tolerance: digits are assigned to colors from 0 to 9 (e.g., black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9). The tolerance band is typically gold for ±5% or silver for ±10%, though other colors can denote tighter tolerances (for example brown for ±1%, red for ±2%, and other tolerances used on precision resistors).

Reading direction and usage: the reading starts from the end with two close-together bands, with the tolerance band usually separated from the other three. This code was widely used for many decades on carbon composition and other resistors but has largely been supplemented by five-band codes for higher precision. It remains common in older equipment and in some modern low-cost resistors.

Variants: some manufacturers apply the fourth band to indicate temperature coefficient (ppm/K) in 4-band parts, while standard 4-band practice designates the fourth band as tolerance. The five-band code adds a third significant digit and a separate tolerance band for higher precision.