Decode resistor colour bands and compute series and parallel networks.
Resistor colour codes follow IEC 60062. Each colour band encodes a digit (0–9), a multiplier power of ten, a tolerance percentage, and (for 6-band precision resistors) a temperature coefficient. Reading the bands from the end closest to the lead, the first 2 (or 3) bands form the mantissa, the next band gives the multiplier, the tolerance band defines the accuracy class, and the optional 6th band specifies temperature stability in ppm/°C.
4-band value
R = (10 × band1 + band2) × multiplier
5/6-band value
R = (100 × band1 + 10 × band2 + band3) × multiplier
Series
Series R = R1 + R2 + ... + Rn
Parallel
1/Rparallel = 1/R1 + 1/R2 + ...
Start from the band closest to a lead. The tolerance band (gold or silver for 4-band) is always at the opposite end. If in doubt, read both ways and look up both values — only one will be a standard E-series value.
Adding parallel paths gives current more ways to flow, reducing the total opposition. The result is always less than the smallest individual resistor.
6-band resistors add a temperature coefficient band, specifying how much the resistance drifts per degree Celsius. Used in precision circuits where thermal stability matters.
The E12, E24, E48, E96 and E192 series define preferred values based on logarithmic spacing. For example, E12 values are: 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 (and their decade multiples).