Resistor Color Code & Ohm's Law Calculator

Decode a resistor's color bands into its resistance and tolerance, or solve Ohm's law (V, I, R, P) from any two known values. Everything runs in this page — nothing is uploaded.

Common questions

What resistor does yellow-violet-red-gold decode to?

This calculator's own default bands — yellow (4), violet (7), red (×100), gold (±5%) — decode to 4.7 kΩ ±5%, one of the most common values in a beginner's kit. The first two bands give the significant digits (47), the third multiplies by 100, and the fourth is the tolerance band.

Why does the LED resistor calculator ask for exactly three values?

Because a series resistor's job is to burn off whatever voltage is left after the LED, at a set current — three knowns (supply voltage, LED forward voltage, target current) solve for the one unknown (resistance). Using the page's own placeholders — 5 V supply, a 2 V forward-voltage LED, 20 mA target — the required resistor is 150 Ω, dissipating 60 mW, for which this calculator recommends a 0.25 W part (it doubles the dissipation before picking a standard wattage, so the resistor runs at roughly half its rated power).

Why does the Ohm's law solver want exactly two fields, not four?

Voltage, current, resistance, and power are tied together by V = IR and P = VI, so any two of the four fix the other two — a third value would either be redundant or contradict the first two, which is why the solver rejects anything but exactly two filled fields. Enter, say, 5 V and 220 Ω and it solves the rest: 22.727 mA and 113.636 mW.