Resistor Color Code Calculator

How This Calculator Works

A 4-band resistor’s color code encodes its resistance value directly on the component itself — two digit bands, a multiplier band, and a tolerance band — so its value can be read without a meter. Select the color printed on each of the four bands, reading from the band closest to one end of the resistor, and this calculator decodes them into the actual resistance in ohms.

Each color stands for a digit, 0 through 9, in a fixed sequence used by every electronics reference (black is always 0, white is always 9). The first two bands give the resistor’s two significant digits; the third band is a multiplier that scales those two digits up or down by a power of ten; the fourth band tells you how far the resistor’s real, manufactured resistance can vary from the value the first three bands encode.

The Formula

$$R = (\vA{D_1} \times 10 + \vB{D_2}) \times \vC{M}$$

where $\vA{D_1}$ and $\vB{D_2}$ are the first and second significant digits (bands 1 and 2), and $\vC{M}$ is the multiplier (band 3). The fourth band’s tolerance percentage doesn’t change $R$ itself — it only defines the range the real resistor’s manufactured value can fall within.

Color Code Reference

Worked Example

Brown – Black – Red – Gold:

1. Band 1 (Brown) is digit $\vA{1}$; band 2 (Black) is digit $\vB{0}$ — together, $10$.
2. Band 3 (Red) is a multiplier of $\vC{100}$ (×10²).
3. Resistance: $R = 10 \times \vC{100} = 1{,}000 \ \Omega = 1 \text{ k}\Omega$.
4. Band 4 (Gold) means a tolerance of ±5% — the real resistor could measure anywhere from 950 Ω to 1,050 Ω.

Yellow – Violet – Orange – Red: digits $\vA{4}$ and $\vB{7}$ give $47$, multiplied by $\vC{1{,}000}$ (×10³) gives $47{,}000 \ \Omega = 47 \text{ k}\Omega$, with a ±2% tolerance.