How to Read Resistor Color Codes
Through-hole resistors use painted color bands to indicate their resistance value and tolerance. This system, established in the 1920s, allows engineers to identify component values regardless of how the resistor is rotated on a circuit board.
The standard 4-band code is the most common. The first two bands represent the significant digits. The third band is the multiplier (how many zeros to add). The final band, which is usually spaced slightly further apart, indicates the manufacturing tolerance.
Understanding Tolerance Bands
No manufacturing process is perfect. The tolerance band tells you exactly how much the actual resistance might deviate from the stated value.
For example, a standard 100Ω resistor with a gold tolerance band (±5%) could safely measure anywhere between 95Ω and 105Ω. In precise analog circuits (like audio equipment or measuring devices), engineers use 5-band or 6-band resistors with tighter tolerances (like brown for ±1%) to ensure accuracy.
SMD Resistor Codes (Surface Mount Devices)
As electronics have shrunk, modern circuit boards primarily use tiny Surface Mount Devices (SMDs). These components are too small for color bands, so they use a short numeric or alphanumeric code stamped on the top.
The most common are 3-digit and 4-digit codes, which function exactly like the color bands: the first digits are the base value, and the last digit is the multiplier (the number of trailing zeros). For high-precision components, the EIA-96 standard uses a special lookup table combining two numbers and a letter to represent complex values in a tiny space.
Last updated: May 2026