Resistor Color Code Calculator

How it is calculated

This tool reads a 4-band resistor. Bands 1 and 2 are digits (black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9). Band 3 is the multiplier, a power of ten (black ×1, brown ×10, red ×100, and so on up to blue ×1,000,000; gold ×0.1; silver ×0.01). Band 4 is the tolerance: brown ±1%, red ±2%, gold ±5%, silver ±10%.

The formula is R = (10 × band1 + band2) × 10^multiplier in ohms. The tool also shows the guaranteed range R × (1 ± tolerance / 100), and writes values in Ω, kΩ or MΩ. Hold the resistor so the tolerance band (gold or silver) is on the right. Five-band and six-band resistors are not covered.

Common mistakes

• Reading the bands from the wrong end. The tolerance band (gold or silver) goes on the right; starting from it reverses the digits.
• Treating the third band as a third digit. On a 4-band resistor it is a multiplier, so orange means ×1,000, not 3.
• Confusing gold and silver as multipliers with gold and silver as tolerances. The same colours mean ×0.1 and ×0.01 in band 3, but ±5% and ±10% in band 4.
• Trusting the marked value for precision work. The actual resistance can be anywhere in the tolerance range, so measure it with a meter when it matters.