Resistor Colour Code Calculator
Decodes a resistor colour code. Pick the number of bands, then the colour of each, and it gives the value, the tolerance and the range the part is actually guaranteed to sit within.
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The formula
4 band: R = (d₁d₂) × multiplier 5 and 6 band: R = (d₁d₂d₃) × multiplier
The colours are a base-10 code: black is 0 through white as 9, in the order of the visible spectrum with black and brown bolted on the front. The multiplier band uses the same colours to mean powers of ten, which is why gold and silver are needed for values below ten ohms.
What to watch out for
Reading the bands the right way round is most of the difficulty:
- Start from the end with bands closest together. The tolerance band sits slightly apart from the rest, usually at the end with the wider gap.
- Gold or silver means you are at the wrong end — with one exception, they only appear as multiplier or tolerance, never as a leading digit.
- Five bands do not mean five per cent. A fifth band means three significant digits, which almost always means a precision part at 1% or better.
When in doubt, measure it. The code tells you what the part claims to be; a meter tells you what it is.
Frequently Asked Questions
How do I read a 4-band resistor?
The first two bands are digits, the third is the number of zeros to add, and the fourth is the tolerance. Yellow-violet-red-gold is 4, 7, ×100 — that is 4.7 kΩ at ±5%.
What is the difference between 4-band and 5-band resistors?
A 5-band resistor has three significant digits instead of two, so it can express values the 4-band code cannot. It usually indicates a precision part with a 1% or tighter tolerance.
Which end do I start reading from?
The end where the bands are grouped closest together. The tolerance band is set slightly apart, and it is often gold or silver — neither of which is ever a first digit.