Resistor Color Code Calculator

A resistor's value is printed on it as coloured bands rather than text because bands can be read from any angle and don't wear off — but that only helps if you remember which colour means which digit, which almost nobody does reliably. This decodes bands into a value, and goes the other way too: type in a target resistance and it finds the actual bands a real component with that value would carry.

The colour code is not arbitrary. Each colour is both a digit (black=0 through white=9) and, in the multiplier position, a power of ten — the reason gold and silver only ever appear as multipliers or tolerance, never as digits, is that they don't fit that pattern; they exist purely to extend the range below 10Ω and to mark tolerance.

A 4-band resistor has two significant digits, a 5 or 6-band one has three — which is why a 5-band resistor is more precise, not just fancier. The 6th band, when present, is a temperature coefficient in parts-per-million per degree, relevant mostly in precision analog circuits where drift with temperature actually matters.

The tolerance band is usually gold or silver and sits alone at one end, with a visibly larger gap before it than between the other bands — that gap is the tell. Start reading from the opposite end. On a resistor where this is genuinely ambiguous (a beige or white tolerance band, evenly spaced bands), the value it decodes to at both orientations is a good sanity check: real resistor values are round numbers in the E12/E24 series, and only one orientation will usually produce one.