Through-hole resistors carry their value as coloured bands because printing legible digits on a 2 mm body is not practical. The code is positional: the first bands are significant digits, the next is a power-of-ten multiplier, and the last is the manufacturing tolerance.
Reading the bands in the right order
Orientation is the part people get wrong. The tolerance band is separated by a slightly wider gap and is usually gold or silver, so put that on the right and read left to right. If both ends look identical, check for a gold or silver band — neither colour is ever used as a first digit.
Four-band resistors
Two digits, a multiplier, a tolerance. Yellow-violet-red-gold is 4, 7, ×100, ±5%, so 4700 Ω, which everyone writes as 4.7 kΩ or 4k7. These are the standard 5% parts in every hobby kit.
Five-band resistors
Three digits, a multiplier, a tolerance. The extra digit gives finer values, which is why precision 1% resistors use this format. Brown-black-black-brown-brown is 1, 0, 0, ×10, ±1%, so 1000 Ω at 1%.
Colour values
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1% |
| Red | 2 | ×100 | ±2% |
| Orange | 3 | ×1k | — |
| Yellow | 4 | ×10k | — |
| Green | 5 | ×100k | ±0.5% |
| Blue | 6 | ×1M | ±0.25% |
| Violet | 7 | ×10M | ±0.1% |
| Grey | 8 | ×100M | ±0.05% |
| White | 9 | ×1G | — |
| Gold | — | ×0.1 | ±5% |
| Silver | — | ×0.01 | ±10% |
What tolerance actually buys you
A 5% 10 kΩ resistor is guaranteed to sit between 9.5 kΩ and 10.5 kΩ. In a voltage divider built from two such parts, the worst-case output error is roughly the sum of the two tolerances, so a divider designed for 2.50 V can legitimately deliver anywhere from about 2.38 V to 2.62 V. If that matters — an ADC reference, a precision bias point — use 1% parts, or measure and trim.
Surface-mount parts
SMD resistors do not use colours. They use printed numeric codes: three digits where the last is the number of zeros (472 is 4700 Ω), four digits for 1% parts (4701 is 4700 Ω), or the EIA-96 system of two digits plus a letter on very small packages. A part marked 0 or 000 is a zero-ohm jumper, not a missing value.