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Resistor color code calculator

Decode resistor color bands into ohms, or generate the bands for a target value.

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Output
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Resistor color code calculator
Paste a row of resistor color band names — "brown black red gold" — and this tool decodes it into a resistance value, a tolerance percentage and the minimum/maximum range that a real resistor with that code can measure. Paste a resistance instead — 4700, 4.7k or 4k7 all work — and it runs the other way, generating the color bands you would need to build or identify that value. Every line is read independently, so a list of codes and a list of target values can be pasted together and processed in the same pass.
The band-count option controls how many colors a generated code uses: 4-band (two significant digits, a multiplier and a tolerance), 5-band (three significant digits and a tolerance) or 6-band, which adds a temperature-coefficient band in parts per million per kelvin. Decoding always reads however many bands you actually typed, from three to six. The value format option controls how resistances are displayed — as a plain number, an engineering suffix like 4.7k, or the mid-letter notation 4k7 that print directly on some resistor bodies. Snapping to the E12 or E24 preferred-value series rounds a target resistance to the nearest value manufacturers actually produce before generating its bands, and shows the same nearest match next to a decoded value for comparison.
A line that is neither a recognizable set of color names nor a parsable resistance value is reported as an error next to that row rather than stopping the rest of the list — a typo on one line never hides the results for the others. The tally under the output reports how many rows were decoded, how many were generated and how many could not be read.
Everything runs locally in your browser; the codes and values you paste are never uploaded anywhere. Copy the result, download it as a .txt file, clear the panel, or send the output back into the input to keep working on it.
FAQ
How do I read the bands on a real resistor?
Type the colors in the order they appear starting from the band closest to one end, separated by spaces — for example "brown black red gold" — and the tool decodes the value, tolerance and min/max range.
What if I only see 3 colored bands?
A 3-band code has two significant digits and a multiplier but no tolerance band, so the tool assumes the standard implicit ±20% tolerance for it.
What does "snap to series" actually change?
When generating bands from a value, it rounds your target to the nearest E12 or E24 preferred value first, so the bands it prints match a resistance that is actually manufactured. When decoding, it just shows the nearest series value alongside the exact reading for comparison — it never changes the decoded result.
Why does it say a row couldn't be read?
Each line must be either 3 to 6 recognized color names or a resistance value like 4700, 4.7k or 4k7. Anything else — an unknown color, a typo, or a value outside the range standard color bands can represent — is reported next to that row while the rest of the list is still processed.
Is my input sent anywhere?
No. Every calculation happens locally in your browser — nothing you type is uploaded or stored on a server.