Resistor Color Code Calculator

Resistor color bands provide a compact, durable way to mark resistance on components too small for ordinary printed numbers. Each color represents a digit, multiplier, tolerance, or temperature coefficient according to the IEC color-code convention. To read a resistor, orient it so the grouped significant bands begin on the left and the usually separated tolerance band sits on the right. The calculator translates that sequence into an electrical value and tolerance range. A four-band resistor uses two significant digits, followed by a multiplier and tolerance. Brown, black, red, and gold means digits one and zero, multiplied by one hundred, with five percent tolerance: 1,000 ohms or 1 kilohm. Five-band precision resistors use three significant digits before the multiplier, allowing values such as brown, black, black, orange, brown to represent 100 times one thousand, or 100 kilohms, with one percent tolerance. Six-band parts add a final temperature-coefficient band, although resistance and tolerance are decoded the same way as a five-band part. Digit colors run from black zero through white nine. For multipliers, the same colors represent powers of ten, while gold multiplies by 0.1 and silver by 0.01. Tolerance colors include brown for one percent, red for two percent, green for 0.5 percent, blue for 0.25 percent, violet for 0.1 percent, gray for 0.05 percent, gold for five percent, and silver for ten percent. A missing tolerance band on older components conventionally indicates twenty percent. Tolerance describes the permitted manufacturing spread around nominal resistance. A 1 kilohm resistor with five percent tolerance may measure from 950 to 1,050 ohms under reference conditions. It does not describe every in-circuit change. Temperature, aging, applied voltage, soldering stress, and self-heating can shift resistance further according to the component specification. Color identification can be difficult on aged parts or under tinted lighting. Brown, red, and orange are easily confused, as are blue, violet, and gray. Confirm uncertain values with a multimeter after isolating the resistor from parallel circuit paths. Never measure resistance on an energized circuit. For safety-critical or precision designs, consult the manufacturer's datasheet for power rating, voltage coefficient, temperature coefficient, pulse handling, and long-term stability in addition to the decoded nominal value.