Resistor Color Code

Decoding a 4-Band Resistor’s Color Bands into Ohms

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.

Key Factors to Consider

• Reading a resistor’s bands in the wrong direction produces a completely different, wrong value. The tolerance band (often gold or silver, and usually spaced slightly apart from the others) is the standard way to identify the correct reading direction — reading from the wrong end swaps which digits are significant and which is the multiplier, so identifying the tolerance band first is worth doing before reading the rest.
• A 5-band resistor uses a similar but distinct scheme with three significant digits instead of two. This calculator is scoped to the widely-used 4-band code — a 5-band resistor (common for higher-precision applications) adds a third digit band before the multiplier, giving finer resolution than the 4-band scheme can express.
• The tolerance band tells you the guaranteed accuracy range, not the resistor’s exact manufactured value. Two resistors with the identical color-coded value (say, both coded as 1kΩ ±5%) can have genuinely different real resistance within that ±5% window — for precision applications, a lower-tolerance resistor (like ±1%) narrows that uncertainty.
• This color code is a widely-adopted international standard (IEC 60062), not just a common convention. The same color-to-digit mapping is used across electronics manufacturing and education worldwide, which is exactly why memorizing the color sequence is such a standard part of electronics fundamentals.

Common Mistakes

• Confusing the multiplier band with a third significant digit. On a 4-band resistor only the first two bands are digits — the third band always scales them by a power of ten, never adds a third digit, which is easy to mix up with 5-band resistors that genuinely do have three digit bands.
• Ignoring the gap before the tolerance band. Manufacturers typically space the tolerance band slightly farther from the others specifically so it can be identified and used to determine reading direction — treating all four bands as evenly spaced makes it easy to read the code backwards.
• Assuming two resistors with the same printed value are electrically identical. Two resistors coded identically can still differ by their full tolerance percentage in either direction — worth remembering when a circuit’s behavior depends on a precise resistance value.

Useful to Know

• Solving for voltage, current, or resistance directly instead of decoding a physical resistor? Ohm's Law Calculator solves for whichever of the three you don’t already know.
• Working out how much voltage a resistor’s wire run loses over distance? Voltage Drop Calculator estimates voltage drop from gauge, length, and material.
• Sizing resistors for a voltage divider circuit? Voltage Divider Calculator calculates the output voltage from a pair of resistor values.