Wirecora resistor guide
How to Read a 3-Band Resistor Color Code
Learn how two significant-digit bands and one multiplier band define a 3-band resistor, including its implicit ±20% tolerance.
Direct answer: A 3-band resistor uses the first two bands as significant digits and the third as the multiplier. Because it has no separate tolerance band, its nominal tolerance is generally interpreted as ±20%.
Band-by-band explanation
- Band 1 · First digitBrown
- Band 2 · Second digitBlack
- Band 3 · MultiplierRed
A 3-band resistor has no tolerance band and is generally interpreted as ±20%.
How it works
- Choose the reading direction that places the two digit bands first and the multiplier band last.
- Convert the first and second colors to digits, keeping their left-to-right order.
- Multiply the two-digit number by the factor represented by the third band, then apply the implicit ±20% tolerance.
Practical example
Brown, Black, Red reads as 10 × 100, so the nominal value is 1 kΩ. With no tolerance band, the expected range is 800 Ω to 1.2 kΩ rather than the tighter range of a four-band part.
Common mistakes
Check these points before relying on a color-code reading or component substitution.
Do not treat the third band as a tolerance band; every visible band in this format contributes to the nominal resistance.
Do not assign gold-band ±5% tolerance to a resistor with only three bands; no tolerance band means ±20% in this code.
Related resistor values
Open a worked color-code page generated from the same resistor engine as the calculator.
Related guides
How to Read a 4-Band Resistor Color Code
Read a 4-band resistor by identifying its first two digits, multiplier, and tolerance, with a complete 220 ohm worked example.
Resistor Tolerance Explained with Practical Ranges
Learn what resistor tolerance means, how to calculate minimum and maximum resistance, and why tolerance is not the same as accuracy in every condition.
Frequently asked questions
Short answers to questions that commonly arise with this resistor topic.
Why is there no tolerance color on a 3-band resistor?
The omitted tolerance band is meaningful: the resistor is generally specified at ±20% tolerance.
How can I identify the reading direction without a tolerance band?
Use band spacing, printed documentation, and whether one direction produces a plausible standard value; verify uncertain parts with a meter.
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