Free tool · Electronics
Resistor Colour Code Calculator
Pick the bands on a 4-band or 5-band resistor to read off its resistance and tolerance. The same colour code used on every leaded resistor, worked out live as you choose each band.
How the colour code works
Each colour stands for a digit from 0 to 9 (black through white), plus two extra colours — gold and silver — used only for the multiplier and tolerance bands. Reading the bands from the end furthest from the tolerance band, a 4-band resistor's value is the two digit bands read as a two-digit number, multiplied by the third band:
d1 and d2 are the digit values (0–9) of the first two bands; the multiplier band scales the result.
A 5-band resistor works the same way with a third digit band for extra precision:
The same idea with three digits instead of two, used on tighter-tolerance resistors.
Worked example
A resistor is banded yellow, violet, red, gold.
Yellow = 4, violet = 7 — the two significant digits.
Red as the third band means multiply by 10², i.e. ×100.
Combine the digits, then apply the multiplier.
Gold as the fourth band is a ±5% tolerance.
Frequently asked questions
What do the colours on a resistor mean?
Each band is a digit, a multiplier or a tolerance, read left to right starting from the band closest to one end. On a 4-band resistor the first two bands are digits, the third is a multiplier (what to multiply those digits by), and the fourth is tolerance. A 5-band resistor uses three digit bands instead of two, for an extra digit of precision.
What's the difference between a 4-band and 5-band resistor?
A 4-band resistor gives two significant digits, so its value is only precise to two figures (e.g. 47 × a multiplier). A 5-band resistor gives three significant digits, which is why 5-band resistors are used where tighter tolerances (1% or better) matter.
What does the tolerance band tell you?
It's how far the actual resistance can be from the value printed by the colour code. Gold means ±5%, silver ±10%, brown ±1%. A resistor coded as 4.7 kΩ with a gold tolerance band could measure anywhere from about 4.465 kΩ to 4.935 kΩ and still be within spec.
Why do some resistors have no visible tolerance band, or a gap instead of one?
A resistor with only 3 bands (two digits and a multiplier, no tolerance band) is an older or lower-cost part with an implied ±20% tolerance. This is rare in modern components, but the calculator's 4-band mode covers it if you treat the missing band as gold or silver, whichever your supplier's datasheet states.
Does this work for surface-mount (SMD) resistors?
No. Surface-mount resistors are usually printed with a numeric code (e.g. "472" for 4.7 kΩ) rather than colour bands, since they're too small to print bands on reliably. This calculator is for through-hole resistors with visible colour bands only.
What's the sixth band on some resistors?
A 6-band resistor adds a temperature coefficient band (in ppm/°C), showing how much the resistance drifts with temperature. It doesn't change the resistance or tolerance reading, so this calculator's 5-band mode still gives the correct value — the sixth band just isn't used.
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