Reading a resistor
Four coloured stripes, no numbers, and a part that looks identical to the one next to it. The code is quick to learn and quicker to forget, so this page is built to be used with a resistor in your hand rather than read once.
Tap a band on the part, then tap a colour. Or take the challenge and work backwards, which is the direction you will actually need.
The rule, in one line
First band is the first digit, second band is the second digit, third band is how many zeros to write after them. The gold stripe on the end is tolerance, ±5%, and it is only there to tell you which end to start reading from.
Most people learn the third band as a "multiplier" and then have to think in powers of ten forever. Counting zeros is the same thing and never needs a second of arithmetic: red-red-brown is 2, 2, one zero — 220 Ω.
The five you will actually meet
| Bands | Value | What it does in your kit |
|---|---|---|
| brown black brown | 100 Ω | A bright LED on 3.3 V |
| red red brown | 220 Ω | The default LED resistor on 5 V |
| orange orange brown | 330 Ω | A gentler LED, and a series resistor for a buzzer |
| brown black red | 1 kΩ | Base resistor for a transistor |
| brown black orange | 10 kΩ | Pull-up, pull-down, and half of every divider |
Four bands with no gold stripe, or five bands instead of four, means a 1% part: three digits and then the zeros. You will see them on breakout boards, rarely in a beginner's kit.
Why the values look random
100, 220, 470, 1 k, 2.2 k, 4.7 k, 10 k. They are not arbitrary: they are the E12 series, twelve steps that are each about 20% bigger than the last, which is the spacing that makes a small set of parts cover any value you calculate to within about 10%. Kits stock E12 values in ±5% parts, which is the gold band.
That is why there is no 200 Ω resistor in your kit. 220 Ω is the nearest value you have, it is 10% high, and for an LED that is the difference between 15 mA and 13.6 mA — which is to say, no difference at all.
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