Resistor Color Code Calculator
Reading a Resistor's Value Without a Meter
Resistors are usually too small to print a legible number on, so their value is encoded instead as a sequence of colored bands — a system that's been standard in electronics since the mid-20th century and still shows up on nearly every through-hole resistor made today. Once you know the code, reading a resistor takes seconds; this calculator decodes the bands into an exact resistance value and tolerance.
The Formula
The first two (or three, on 5-band resistors) bands form the significant digits, and the next band multiplies them:
Tolerance = ± (value of the tolerance band)
A 4-band resistor uses 2 significant digits; a 5-band resistor uses 3, giving finer precision before the multiplier is applied.
Where This Calculation Matters
- Circuit repair and reverse-engineering — identifying an unlabeled resistor's value when swapping a failed component or tracing an existing circuit.
- Component sorting — quickly verifying a bag of mixed resistors matches its labeled value before using them in a build.
- Electronics education — learning and checking the standard color code without needing a multimeter on hand.
- Kit and prototype assembly — confirming the correct resistor is being placed in a breadboard or PCB position before soldering.
Color Code Reference
| Color | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1% |
| Red | 2 | ×100 | ±2% |
| Orange | 3 | ×1,000 | — |
| Yellow | 4 | ×10,000 | — |
| Green | 5 | ×100,000 | ±0.5% |
| Blue | 6 | ×1,000,000 | ±0.25% |
| Violet | 7 | ×10,000,000 | ±0.1% |
| Gray | 8 | ×100,000,000 | ±0.05% |
| White | 9 | ×1,000,000,000 | — |
| Gold | — | ×0.1 | ±5% |
| Silver | — | ×0.01 | ±10% |
| None | — | — | ±20% |
Brown-Black-Red-Gold decodes to 1,000 Ω (1 kΩ) ±5% — a very common value. Yellow-Violet-Orange decodes to 47,000 Ω (47 kΩ).
How to Use This Calculator
- Choose 4-Band Resistor or 5-Band Resistor.
- Select the color for each significant digit band (band 1, band 2, and band 3 on 5-band resistors).
- Select the Multiplier band color.
- Select the Tolerance band color (defaults to None, ±20%, if left unset).
- Select Calculate to see the resistance value with proper unit (Ω, kΩ, or MΩ) and tolerance.
Related Calculations
Working with capacitors on the same circuit? Use the Capacitor Charge Calculator. Need general storage or bandwidth unit conversions instead? See the Storage Calculator.