The resistor color code

A standard 4-band resistor reads in order: digit, digit, multiplier, tolerance. The digit colors run: Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9. The multiplier band uses the same colors as powers of ten.

Worked example: Red-Red-Brown. Red = 2, Red = 2 → digits "22". Brown multiplier = ×10. So 22 × 10 = 220Ω. The fourth band (gold = ±5%, silver = ±10%) tells you how close to that nominal value the real part is — a 220Ω ±5% part could actually be anywhere from 209Ω to 231Ω.