Resistor Color Code
Decode resistor color bands to resistance + tolerance.
Overview
The Resistor Color Code decoder translates the coloured bands printed on a resistor into a resistance value with tolerance. Pick 3, 4 or 5 bands, click each colour and the decoder reports the resistance in ohms along with the tolerance percentage.
It is built for electronics hobbyists, students just learning the bands, technicians prototyping circuits and anyone who has reached into a parts drawer and pulled out a mystery resistor. The encoding is standard but the colours are easy to misread when you're tired.
How it works
In a 4-band resistor the first two bands are significant digits, the third is a power-of-ten multiplier and the fourth is tolerance. Black = 0, brown = 1, red = 2, orange = 3, yellow = 4, green = 5, blue = 6, violet = 7, grey = 8, white = 9. For 5-band resistors the first three are digits and the fourth is the multiplier.
For example, brown-black-red-gold means 10 * 10^2 = 1000 Ω with 5% tolerance. The decoder accepts either band order and warns when the colour sequence is ambiguous (some 5-band patterns can be read backwards into a different value).
Examples
Brown, Black, Red, Gold → 1 kΩ ± 5%
Red, Red, Orange, Gold → 22 kΩ ± 5%
Yellow, Violet, Black, Brown, Brown (5-band) → 4.70 kΩ ± 1%
Brown, Black, Black, Gold (3-band) → 10 Ω
FAQ
How do I tell which end is band 1?
The tolerance band (gold or silver) is usually farthest from the rest. Read with band 1 on the left.
What if there's no tolerance band?
A 3-band resistor has 20% tolerance by default. Modern resistors are almost always 4 or 5 band.
Why is 4.7 kΩ written as 4K7 elsewhere?
The letter replaces the decimal point in industry shorthand. The colour code still decodes to the same 4700 Ω.
Are SMD resistors colour-coded?
No, surface-mount components use numeric codes like 103 for 10 * 10^3 = 10,000 Ω. The colour band system is for through-hole resistors.
Are there 6-band resistors?
Yes — the sixth band is the temperature coefficient (ppm/°C). This decoder focuses on 3-5 band resistors which cover almost all hobbyist parts.