Decode a 4-band resistor’s colour code into its resistance and tolerance.
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How do you read a 4-band resistor color code?
Resistance = (digit1 × 10 + digit2) × multiplier, and the fourth band gives the tolerance (gold ±5%, silver ±10%). Read the bands from the end where they are grouped closest together. For example, brown, black, red, gold reads (1, 0, ×100, ±5%) = 1,000 Ω (1 kΩ) ±5%. The tool reports the value in ohms, kΩ or MΩ.
Understanding your result
Read the bands from the end where they’re grouped closest together; the tolerance band (often gold or silver) is on the opposite end.
Formula and method
Resistance = (digit1 × 10 + digit2) × multiplier. The fourth band gives the tolerance (gold ±5%, silver ±10%).
Assumptions and limitations
It decodes the standard 4-band resistor: two digit bands, a multiplier and a tolerance band. It does not read 5- or 6-band precision resistors with an extra significant figure or a temperature-coefficient band, and it relies on you identifying the band colours correctly and reading them in the right order.
Worked example
Brown, black, red, gold reads (1, 0, ×100, ±5%) = 1,000 Ω (1 kΩ) ±5%.
How to use this tool
- Select the colour of each of the four bands.
- Read the resistance and tolerance instantly.
About the Resistor Color Code Calculator
The Resistor Color Code Calculator decodes a standard 4-band resistor: two digit bands, a multiplier and a tolerance, giving the resistance and its range.
Who should use this tool
Electronics hobbyists, engineering students and repair technicians who have a physical 4-band resistor in hand and want to read off its resistance and tolerance directly from the four colour bands without memorising or hunting through the full colour code chart.
Benefits
- Decodes the four colour bands into resistance and tolerance
- Shows the resistance range implied by the tolerance
- Removes the need to memorise the colour code
- Everything runs on your device, so your inputs stay private
Practical use cases
- Identifying an unlabelled resistor pulled from a parts bin
- Checking a resistor value before soldering it in
- Learning to read resistor colour bands for a course
- Confirming a replacement matches the original component
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Frequently asked questions
What does the gold band mean?
As the fourth band it means ±5% tolerance. As a multiplier band it means ×0.1.
How do I know which end to start reading from?
Read from the end where the bands are grouped closest together. The tolerance band, often gold or silver, sits slightly apart at the opposite end. So the first two bands give the digits, the third is the multiplier, and the gold or silver band is read last.
What does the tolerance band tell me?
It shows how far the true resistance may vary from the marked value, with gold meaning plus or minus 5% and silver plus or minus 10%. A 1000 ohm resistor with a gold band could actually measure anywhere between 950 and 1050 ohms.