4-Band Resistor Color Code

How to use this calculator

A 4-band resistor encodes its value in four color rings read from the end nearest the other bands (the tolerance band — gold or silver — is always last and slightly spaced). Choose each band's color from the dropdowns: the first two bands give the two significant digits, the third band is the power-of-ten multiplier, and the fourth band is the manufacturing tolerance. The resistor illustration and the decoded value update the instant you change a band, and each digit, multiplier and tolerance is shown in its own band color so you can cross-check your reading against the physical part.

What the value means in a circuit

The nominal resistance (in Ω, kΩ or MΩ) tells you how strongly the resistor opposes current, per Ohm's law V = I·R. The tolerance is the manufacturer's guaranteed band around that value — a 2.2 kΩ ±5% part will measure anywhere from 2.09 kΩ to 2.31 kΩ — which is why precision circuits specify tighter (blue/violet) tolerances and why the acceptable range is shown. In a current-limiting or voltage-divider application, the actual resistance sets the current and node voltage, so understanding both the nominal value and its tolerance is what separates a circuit that simply works from one that works reliably part-to-part.