Resistor Color Code Calculator

Decoding a 4-band resistor comes down to reading four stripes of color and translating them into ohms. The calculator works in that direction: pick the four colors and it returns the nominal value and the tolerance range. For anyone building, repairing, or studying circuits, getting this right the first time matters: a single misread band can mean ordering the wrong component or chasing a fault that was never there.

The color scheme is the international code in IEC 60062 (Marking codes for resistors and capacitors, 2016 edition). On a 4-band part, the first two bands give the significant digits, the third band sets the multiplier as a power of ten, and the fourth band states the tolerance. Every color maps to one specific digit, multiplier, or tolerance percentage, so the conversion between the painted stripes and a numerical resistance is fully systematic once you know the order. The calculator offers multipliers from silver (×0.01) to blue (×1,000,000) and the tolerances brown ±1%, red ±2%, gold ±5% and silver ±10%; a resistor with only three bands is ±20%.

Reading direction is where most errors creep in. The tolerance band usually sits a little wider or with a noticeable gap, which tells you which end to start from; flip the resistor and you can swap the first significant digit with the last and land on a wildly wrong value. Brown, red, and orange are the colors most often confused under dim or yellow light, so confirm those shades against a known-good reference before you trust the reading.