Resistor Color Code Calculator

How resistor bands work

Through-hole resistors are too small to print a number on, so their value is painted as coloured bands. Reading from the end opposite the wider gap: the first two bands (three on precision 5- and 6-band parts) are significant digits, the next band is a power-of-ten multiplier, then comes the tolerance, and 6-band resistors add a temperature coefficient in ppm/K.

Digits run black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold and silver as multipliers mean ×0.1 and ×0.01; pink (×0.001) was added in IEC 60062:2016. Common tolerances are gold ±5 %, silver ±10 %, brown ±1 % and red ±2 %; a missing band means ±20 %.

Worked example

Yellow, violet, orange, gold: digits 4 and 7, multiplier 10³, tolerance ±5 %. That is 47 × 1,000 = 47,000 Ω = 47 kΩ ±5 %, so any part between 44.65 kΩ and 49.35 kΩ is within spec.

The value is computed exactly as the standard describes:

R = (d₁d₂[d₃]) × 10^m     tolerance = ±t %
Rmin = R × (1 − t/100)    Rmax = R × (1 + t/100)

The reverse lookup parses values written with SI prefixes (470k, 2.2M) or with the letter as decimal point (4k7, 0R22), as in IEC 60062 clause 4, then finds the digit and multiplier bands. If a value needs more significant digits than the chosen band count allows, it says so instead of rounding silently.