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Resistor Color Code Calculator

Decode 4, 5 and 6-band resistor color codes into resistance, tolerance and temperature coefficient.

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Resistor Color Code Calculator is free to use as often as you like, directly from this page. Its place is under Electronics; Capacitor code calculator (decoder) and LED resistor calculator answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Resistor Color Code Calculator?

Decode 4, 5 and 6-band resistor color codes into resistance, tolerance and temperature coefficient.

When would I actually use this?

At the bench: sizing a resistor for an LED, reading a colour band, working out a divider ratio, and checking a part will not cook.

What is the most common mistake?

Choosing a resistance and forgetting the power rating. A value that is electrically right will still burn if the package cannot dissipate what passes through it — check the watts as well as the ohms.

How is Resistor Color Code Calculator different from Capacitor code calculator (decoder)?

They sit next to each other but answer different questions: Capacitor code calculator (decoder) is the one to open when you need it to the three-digit code printed on a ceramic capacitor is picofarads: the first two digits times ten to the third. Enter the code (104 → 100 nF) and get the value in pF, nF and µF. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

LED resistor calculator is the closest one after this: Find the series resistor needed to drive an LED from a supply voltage.

What else is worth having open alongside it?

Parallel resistor calculator and Series resistor calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Ohm's law and the divider formulas are exact. Colour bands follow the IEC standard; real components carry a tolerance, so a nominal value and a measured one will not match exactly.

Further reading

All guides →
ExplainerResistors in Series and in Parallel: The Formulas, and the Three Things They Do Not Tell YouSeries adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.ExplainerScreen Resolution, Pixel Density, and the Numbers Marketing UsesA diagonal plus an aspect ratio gives you width and height by Pythagoras, and the answer is not what the marketing implies: a 27-inch 21:9 has 16.2% less area than a 27-inch 16:9. Then pixels per degree, which shows the highest-PPI phone is not the sharpest thing you own.How-toHow to Calculate an LED Series ResistorSize the series resistor for any LED with one formula: R = (Vs − Vf) / I. Follow the steps, see a worked 5 V example, and pick the right resistor.ExplainerWhat Is Ohm's Law? V = I × R Explained SimplyOhm's law links voltage, current, and resistance with one equation: V = I × R. Learn the triangle trick and see worked examples.ExplainerThe Voltage Divider: The Formula Is Trivial, the Assumption Behind It Is NotVout = Vin·R2/(R1+R2) is only true when nothing is connected to the output. Draw current and the voltage collapses, by an amount that follows one exact law. Here is that law, the ten-times rule checked against it, and why a lower-resistance divider costs you power forever.ExplainerWhat Is Voltage Drop? Why Long Wires Lose VoltageVoltage drop is the voltage lost along a wire due to its resistance. Learn how length, gauge, and current affect it, and why it matters for your circuits.