Resistor Colour Code Calculator

The first two bands are significant digits, the third is the multiplier and the fourth is the tolerance. Red, red, brown, gold reads as 2 and 2 giving 22, multiplied by 10 for 220 Ω, with the gold band meaning ±5%. The calculator decodes the bands as you select them and also shows the minimum and maximum resistance the tolerance allows.

A 5-band code carries three significant digits instead of two, which is needed for precision parts. Four bands suit the coarser E12 and E24 ranges at ±5% or ±10%, while ±1% and tighter resistors use five bands to express the finer E96 values. For example brown, black, black, red, brown decodes as digits 1, 0, 0 with a ×100 multiplier: 10 kΩ at ±1%.

Start from the band nearest one end of the body; the tolerance band usually sits slightly apart at the other end. Gold or silver can only be a tolerance or multiplier band, never a first digit, so if a gold or silver band sits at one end, read from the opposite end. If the value looks implausible, try decoding in the reverse order and pick the value that exists in a standard series.

Tolerance is the manufacturer's guaranteed limit on the true resistance. A 220 Ω resistor at ±5% can measure anywhere between 209 Ω and 231 Ω and still be in specification. The calculator displays this minimum and maximum alongside the nominal value. Where a circuit depends on an accurate ratio, such as a voltage divider feeding a measurement input, choose ±1% five-band parts rather than ±5%.

Standard resistors follow preferred number series (E12, E24, E96) in which each value is spaced from the next by roughly the tolerance percentage, so the range covers every possible value without wasteful overlap. The E24 series steps through 10, 11, 12, 13, 15 and so on up to 91 in each decade, which produces the familiar 220, 470 and 680 Ω values stocked by every distributor.