Engineering · Electronics · Electronics
Resistor Color Code Calculator
Decode 4-band and 5-band resistor color codes to determine resistance value and tolerance.
Calculator
Formula
For a 4-band resistor: D1 is the first significant digit (band 1), D2 is the second significant digit (band 2), M is the multiplier exponent (band 3), and band 4 is the tolerance. For a 5-band resistor: R = (D1 × 100 + D2 × 10 + D3) × 10^M, where D3 is a third significant digit from band 3, M is the multiplier from band 4, and band 5 is the tolerance.
Source: IEC 60062: Marking codes for resistors and capacitors, International Electrotechnical Commission.
How it works
Resistors are marked with colored bands because printing numerical values on small cylindrical components is impractical. The IEC 60062 standard defines a universal color coding system where each color corresponds to a digit (0–9), a multiplier (10⁻² to 10⁹), or a tolerance value. 4-band resistors are the most common general-purpose type, while 5-band resistors provide an additional significant digit for greater precision and are often found in precision and military-grade applications.
For a 4-band resistor, the formula is: R = (D₁ × 10 + D₂) × M, where D₁ and D₂ are the digit values of the first two bands and M is the multiplier from the third band. The fourth band indicates tolerance. For a 5-band resistor, the formula extends to: R = (D₁ × 100 + D₂ × 10 + D₃) × M, with the fifth band indicating tolerance. The color-to-digit mapping follows the mnemonic sequence: Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (7), Grey (8), White (9). Gold and Silver are used only as multipliers (×0.1 and ×0.01) or tolerance indicators (±5% and ±10%).
Knowing the exact resistance range — the nominal value adjusted by the tolerance percentage — is critical for circuit design. A 1 kΩ ±5% resistor can have a true value anywhere from 950 Ω to 1,050 Ω. This matters greatly in precision voltage dividers, filter circuits, and amplifier bias networks. Engineers use this calculator during prototyping, PCB design review, component verification, and field repair work to confirm that a physical resistor matches the design specification before soldering it in place.
Worked example
Example 1: 4-Band Resistor — Brown, Black, Red, Gold
Band 1 (Brown) = digit 1. Band 2 (Black) = digit 0. Band 3 (Red) = multiplier ×100. Band 4 (Gold) = tolerance ±5%.
Resistance = (1 × 10 + 0) × 100 = 1,000 Ω = 1 kΩ. Minimum = 1,000 × 0.95 = 950 Ω. Maximum = 1,000 × 1.05 = 1,050 Ω.
Example 2: 5-Band Resistor — Red, Violet, Green, Brown, Brown
Band 1 (Red) = digit 2. Band 2 (Violet) = digit 7. Band 3 (Green) = digit 5. Band 4 (Brown) = multiplier ×10. Band 5 (Brown) = tolerance ±1%.
Resistance = (2 × 100 + 7 × 10 + 5) × 10 = 275 × 10 = 2,750 Ω = 2.75 kΩ. Minimum = 2,750 × 0.99 = 2,722.5 Ω. Maximum = 2,750 × 1.01 = 2,777.5 Ω. This precision resistor is suitable for use in instrumentation amplifier gain-setting networks.
Limitations & notes
This calculator covers standard 4-band and 5-band resistors per IEC 60062. It does not support 3-band resistors (which assume ±20% tolerance), 6-band resistors (which add a temperature coefficient band), or specialty SMD (surface-mount device) resistors that use a 3- or 4-digit numeric EIA-96 code instead of color bands. Color interpretation can be affected by lighting conditions, aging, and print quality — always verify critical components with a multimeter. The calculator assumes bands are read left-to-right in the standard orientation; resistors with non-standard band spacing or military markings may require additional reference materials.
Frequently asked questions
How do I know which end of a resistor to start reading from?
The first band is typically closest to one end of the resistor body. On 4-band resistors, the tolerance band (Gold or Silver) is usually on the right side, so you read from left to right starting at the opposite end. On 5-band precision resistors, the first band is often closer to one lead than the others. When in doubt, use a multimeter to confirm.
What does a resistor with no tolerance band mean?
A 3-band resistor with no fourth band has an implied tolerance of ±20%. These are older, general-purpose components and are rarely used in modern precision designs. The IEC 60062 standard treats the absence of a tolerance band as a ±20% classification.
What is the difference between 4-band and 5-band resistors?
A 4-band resistor encodes two significant digits plus a multiplier and tolerance, giving values in the standard E12 or E24 series. A 5-band resistor adds a third significant digit, enabling values from the E96 series (96 values per decade) with tolerances of ±1% or better. 5-band resistors are used in precision circuits where tighter resistance accuracy is required.
Why do some resistors have Gold or Silver as the third band in a 4-band code?
Gold (×0.1) and Silver (×0.01) multipliers allow resistors below 10 Ω to be encoded. For example, a Brown-Black-Gold-Gold resistor is 1 Ω ±5%. These small-value resistors are commonly used as current-sense resistors in power circuits.
How accurate is color code reading compared to using a multimeter?
Color codes give the nominal rated value; a multimeter measures the actual resistance of a specific component, which will differ based on manufacturing tolerance, temperature, and aging. For any circuit requiring accuracy better than ±5%, always measure with a calibrated multimeter or LCR meter rather than relying solely on the color code.
Last updated: 2025-01-15 · Formula verified against primary sources.