Resistance Color Code Calculation

In the electronics domain, correct identification of resistors plays a crucial role. This is where resistor color codes come into use. Resistor color codes are a fast and practical system for calculating resistance value, tolerance, and temperature coefficient. Resistors used in electrical circuits are specifically designed to control or limit current. However, reading numerical values on small components is not always possible. For this reason, a color-band coding system is used. Resistor color codes not only define the resistance value but also include key parameters such as tolerance and temperature sensitivity. More detailed information about resistor coding, color bands, and resistance calculations can be found in the rest of this article.

What Are Resistor Color Codes?
Resistors on the market are commonly classified as 4-band, 5-band, or 6-band resistors. Resistors with 4 colored stripes are referred to as 4-band resistors, while those containing 5 colored stripes are called 5-band resistors. The system that expresses resistor value using these bands is called the resistor color code. Using the color bands on a resistor, you can calculate the resistance value (in ohms), tolerance (deviation rate), and temperature sensitivity.

How Does Resistor Color Coding Work?
Resistor color coding uses numeric values assigned to each color. These numeric values allow practical calculation. Resistance color code calculation varies depending on the number of bands on the resistor. The numeric values for resistor color codes are:

Color    Digit    Multiplier    Tolerance
Black    0    10^0 (1)    ±20%
Brown    1    10^1    ±1%
Red    2    10^2    ±2%
Orange    3    10^3    N/A
Yellow    4    10^4    N/A
Green    5    10^5    ±0.5% (rare)
Blue    6    10^6    ±0.25% (rare)
Violet    7    10^7    ±0.1% (very rare)
Gray    8    10^8    ±0.05% (very rare)
White    9    10^9    N/A
Gold    N/A    0.1    ±5%
Silver    N/A    0.01    ±10%

Multiplier value is calculated as 10 raised to the power of the digit value of the color. For example, orange corresponds to 10^3 = 1000. Tolerance indicates the deviation margin of the resistor.

How to Calculate a 4-Band Resistor?
The first two bands are placed side-by-side to form a 2-digit number. The third band represents the multiplier. The fourth band defines tolerance.

Formula:
Resistance Value = (2-digit number) × (Multiplier)

Example:
Bands: Yellow (4), Violet (7), Red (10^2 = 100), Green (tolerance ±5%)
Result: 47 × 100 = 4700 ohms (4.7 kΩ)
Tolerance: 5% of 4700 = 235
Tolerance range: 4465 – 4935 ohms

How to Calculate a 5-Band Resistor?
The only difference from a 4-band resistor is that the first three bands form a 3-digit number. The fourth band is the multiplier, and the fifth band is tolerance.

Formula:
Resistance Value = (3-digit number) × (Multiplier)

Example:
First 3 bands: Red (2), Black (0), Black (0) → 200
4th band: Brown (10^1 = 10)
5th band: Silver (±10% tolerance)
Result: 200 × 10 = 2000 ohms (2 kΩ)
Tolerance: 10% of 2000 = 200
Tolerance range: 1800 – 2200 ohms

As stated, standard SMD resistors typically use 3 or 4-digit numeric coding instead of color bands.