Resistor Color Code Calculator

Which end do you start from

Color bands are grouped toward one end of the body, leaving a wider gap before the final band. Read from the crowded end. If the resistor has a gold or silver band, that is the tolerance band and it goes on the right — gold and silver are never used as the first digit, so their presence alone tells you the orientation. On some 5-band precision parts every band is a color, and then the safest move is to measure the part with a meter rather than guess the direction, because reading backwards gives a plausible but wrong value.

What each band count means

A 4-band resistor gives two significant digits, a multiplier and a tolerance. A 5-band gives three significant digits, a multiplier and a tolerance — used where 1% parts need the extra resolution. A 6-band adds a temperature coefficient in parts per million per kelvin, which tells you how far the value drifts as the part heats up. Brown at 100 ppm/K means a 10 kΩ resistor moves by 1 Ω for every 1 °C rise, which is irrelevant in a pull-up and significant in a precision reference.

Tolerance is the number that matters

The nominal value is a label; the tolerance is the promise. A 100 kΩ ±5% resistor is only guaranteed to sit between 95 kΩ and 105 kΩ, and manufacturers will happily ship parts at the edge of that band. Where a divider or a timing network depends on the ratio of two resistors, stack the worst cases in both directions before deciding the circuit works. This calculator prints the guaranteed minimum and maximum for exactly that reason.

Why the values look arbitrary

Standard resistors come in preferred values — the E-series — spaced so that consecutive values overlap at their tolerance edges and cover the whole range without gaps. E24 is the ±5% series and gives 24 values per decade: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24 and so on. E96 is the ±1% series with 96 values per decade. That is why 4.7 kΩ exists and 5 kΩ generally does not. The calculator flags the nearest standard value, so if your decoded number is far from any E-series member, you have probably read a band wrong.

When the colors are unreadable

Heat, age and cheap paint all shift colors; brown, red and orange are easy to confuse under warm light, and on small parts violet and blue look identical. Any decoded value should sanity check against a meter before you rely on it. A resistor that has run hot enough to discolour its body has usually drifted in value as well, so replace rather than re-use it.

Frequently Asked Questions