Red, red, brown
- Input
- red-red-brown
- Expected output
- 220R ±20%
22 × 10 = 220 Ω. At ±20% the part can measure from 176 to 264 Ω.
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3 band resistor color code
A resistor with three colored bands has no tolerance band, and that absence is the information: the tolerance is ±20%. The first two bands are digits and the third is the multiplier. Red, red, brown reads 22 × 10, which is 220 Ω, and the real value can land anywhere between 176 Ω and 264 Ω.
22 × 10 = 220 Ω. At ±20% the part can measure from 176 to 264 Ω.
10 × 100 = 1,000 Ω, with a window of 800 to 1,200 Ω.
47 × 1,000 = 47,000 Ω, and the tolerance lets the real value sit between 37.6 and 56.4 kΩ.
10 × 1,000 = 10,000 Ω, covering 8 kΩ to 12 kΩ.
33 × 100 = 3,300 Ω, with a window of 2,640 to 3,960 Ω.
Start from the end opposite the tolerance band. The tolerance band is usually gold or silver (or visibly set apart from the rest with a wider gap), so it's always read last, and tells you which end to begin at.
±20%. By convention, a missing tolerance band stands for that value, the least precise one on the color chart.
Multiplier. Only the first two bands are digits. If the third band is black, the multiplier is ×1, as in red, red, black, which gives 22 Ω.
On older parts, such as those on old boards. They are read with the same color table used on other resistors today, just without the tolerance band.
Measure it with a multimeter, out of the circuit. The reading must fall inside the ±20% window. If it falls outside, the part has aged or was read backwards.
This is a standard E24 value (typical tolerance ±5%).
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