Resistor Colour Code Calculator

In short A resistor's colour bands are a number in base ten with the digits written as colours. On a four-band part the first two bands are digits, the third is how many zeros to add, and the fourth is the tolerance — so brown-black-red-gold is 1, 0, two zeros, giving 1,000 Ω at ±5%. Five and six band parts add a third digit for precision and, on six-band, a temperature coefficient. The digit colours run black, brown, red, orange, yellow, green, blue, violet, grey, white for 0 to 9, and the middle of that run is not arbitrary: 2 to 7 are the visible spectrum in order, which is the part worth actually memorising. Two practical points save more time than the code itself. First, reading from the wrong end gives a plausible but wrong answer, so find the reference: gold and silver only ever appear as a multiplier or a tolerance, never as a digit, and the tolerance band is spaced slightly further from the others. A first band of black is impossible, because a value never starts with zero. Second, check the result against the preferred series. Resistors are only made in the IEC 60063 values — E24 for ±5% parts — so a reading that does not land on one of those is almost always a misread band rather than an unusual resistor.