Laptop boards are almost entirely surface-mount, but colour-coded through-hole resistors still turn up in desktop power supplies, older motherboards, monitors, chargers and test leads you build yourself. The colour bands are easy to misread under poor light. Pick the bands here and the calculator shows the value, the tolerance range and a preview, so you can compare it with the part in your hand.
How to use it
- Choose 4, 5 or 6 bands.
- Hold the resistor with the tolerance band — often gold or silver, and set slightly apart — on the right.
- Select each band from left to right.
- Compare the preview with the part, then read the value and its range.
How the code works
| Bands | Meaning |
|---|---|
| 4 | digit, digit, multiplier, tolerance |
| 5 | digit, digit, digit, multiplier, tolerance |
| 6 | digit, digit, digit, multiplier, tolerance, temperature coefficient |
The digits run black (0) to white (9). The multiplier is a power of ten — the same colour order, plus gold for ×0.1 and silver for ×0.01. Tolerance is usually gold (5 %) on four-band parts and brown (1 %) on five-band precision parts.
Worked example
Yellow, violet, red, gold on a four-band resistor: 4, 7, ×100, ±5 % — 4.7 kΩ, anywhere from 4.465 kΩ to 4.935 kΩ. Out of circuit, your meter should read inside that range. The same value on an SMD part would be marked 472; that system is decoded by SMD Resistor Code Calculator.
Reading tricky parts
- Which end is first? The first band is closer to the end of the body. Gold and silver are never first.
- Brown, red or orange? Heat-darkened resistors are hard to read. Measure out of circuit and compare with the candidates.
- Blue-bodied resistors are often metal film with five bands; beige bodies are often carbon film with four.
When the colours are burnt beyond reading, the schematic is the only reliable source. Measuring is covered in How to Test a Resistor with a Multimeter (In and Out of Circuit).
FAQ
Why does my resistor have five bands?
Five-band resistors are precision parts with three significant digits, usually 1 % tolerance or better.
What does the sixth band mean?
The temperature coefficient: how much the value changes per degree, in parts per million.
My measured value is outside the range. Is it bad?
If measured out of circuit at room temperature, yes — it has drifted. In circuit, parallel paths can lower the reading.