Resistor Color Code Calculator
Decode a 4-band resistor colour code into resistance and tolerance.
Results update as you type.
About this calculator
A 4-band resistor encodes its value in coloured bands: the first two bands are digits, the third is a power-of-ten multiplier and the fourth is the tolerance. The resistance is (10 × digit1 + digit2) × multiplier ohms. Pick the colour of each band to read off the value.
Frequently asked questions
How do resistor colour bands work?
The first two bands give the significant digits, the third is a ×10ⁿ multiplier and the fourth is the tolerance. Brown-Black-Red-Gold = 1, 0, ×100, ±5% = 1 kΩ ±5%.
What does the tolerance band mean?
Tolerance is how far the real resistance may stray from the nominal value. A ±5% 1 kΩ resistor can measure anywhere from 950 Ω to 1050 Ω.
How does reverse mode pick the bands?
It rounds your target to the nearest value the digit bands can express, then chooses the multiplier so the reading matches — the same colours you would read off a real resistor of that value.
Results are estimates for general guidance only, not financial, medical or tax advice.